How should we live?
This is an important question. And like all other questions, we should answer it from a biblical worldview. Our morality, like our ontology and our epistemology, shouldn’t be defined by philosophy distinct from God’s revelation. Rather, our morality should be based upon and regulated by a worldview grounded in God’s Word.
Over against the autonomous ethical philosophies of men, where good and evil are defined by sinful speculation, the Christian ethic gains its character and direction from the revealed word of God, a revelation which harmonizes with the general revelation made of God’s standards through the created order and man’s conscience. 
The purpose of this article is to outline the basics of a Christian ethic. I rely heavily on the works of Christian thinkers such as Greg Bahnsen, Cornelius van Til, R.C. Sproul, R.J. Rushdoony, and many more (I’ll give references for further study). But note: I’m not providing a new perspective on the age-old questions of morality. Rather, I’m outlining what I consider to be the basics of a Christian ethic.
Internet Encyclopedia of Philosophy defines ethics as follows:
The field of ethics (or moral philosophy) involves systematizing, defending, and recommending concepts of right and wrong behavior. Philosophers today usually divide ethical theories into three general subject areas: metaethics, normative ethics, and applied ethics. Metaethics investigates where our ethical principles come from, and what they mean. Are they merely social inventions? Do they involve more than expressions of our individual emotions? Metaethical answers to these questions focus on the issues of universal truths, the will of God, the role of reason in ethical judgments, and the meaning of ethical terms themselves. Normative ethics takes on a more practical task, which is to arrive at moral standards that regulate right and wrong conduct. This may involve articulating the good habits that we should acquire, the duties that we should follow, or the consequences of our behavior on others. Finally, applied ethics involves examining specific controversial issues, such as abortion, infanticide, animal rights, environmental concerns, homosexuality, capital punishment, or nuclear war. 
So ethics can be divided into three general categories: metaethics, normative ethics, and applied ethics. For the purposes of this article, we’re mostly interested in the first two: metaethics and normative ethics.
Keep this difference in mind: normative ethics are about the norms themselves. Metaethics is about the grounding of those norms.
But before we discuss the separate fields of metaethics and normative ethics, let’s talk about ethics in general, and the overarching theme of Christian ethics.
Ethics in general.
In his book, By This Standard, Bahnsen makes the following remark: “all of life is ethical.” 
All human behavior and character is subject to appraisal according to moral value; every one of our attainments (whether they be aims that are fulfilled or character traits that are developed) and every one of our actions (whether they be mental, verbal, or bodily behavior) expresses an unspoken code of right and wrong … All of life is ethical. 
The truth of this is evident: no matter what we’re doing, in the back of our minds, we’re always using some sort of standard to judge our actions and the actions of others in a moral sense. Why do we dislike mean people? Because we cannot shake the feeling that they really shouldn’t be mean – whether they want to or not. Why do we care about the ethical values of politicians? Because ethics matters to us (more so even than prosperity). Why do we feel guilty when we lie? Because we know we shouldn’t do that.
Francis Schaeffer writes:
People are unique in the inner life of the mind – what they are in their thought world determines how they act. This is true of their value systems and it is true of their creativity. It is true of their corporate actions, such as political decisions, and it is true of their personal lives. The results of their thought world flow through their fingers or from their tongues into the external world. This is true of Michelangelo’s chisel, and it is true of a dictator’s sword. 
Thoughts determine actions. The values we hold determines the actions we take – the people we are. If we value God’s law, we will be godly people. But if we value nothing but our own pleasure the end result will be a society filled with satanic hedonists who care nothing for what’s truly right, nothing for the pain they inflict, and nothing for the wrong they do.
But how do we avoid this? How do we live good lives – lives that are really good, not merely subjectively desirable? By what standard shall we judge our lives and the lives of others?
Making moral judgments requires a standard of ethics. Have you ever tried to draw a straight line without the aid of a standard to follow, such as a ruler? As good as your line may have seemed initially, when you’ve placed a straight-edge up to it, the line was obviously crooked ... If we are going to be able to determine what kinds of persons, actions, or attitudes are morally good, then we will need a standard here as well. Otherwise we will lead crooked lives and make inaccurate evaluations. What should our ethical standard be? ... How does one know and test what is right and wrong? 
For making good decisions – for making ethical decisions – we need to know what good really is. We need to know the ultimate standard of goodness. This is the purpose of ethics: establishing how we should live – establishing the moral standard.
Who is to rule the earth?
All societies are Theocracies. The only thing that separates one society from another, is 'who is Theo?’ 
We’ve established what ethics is all about (the question of how we should live), but there’s something more to be said about the Christian view of ethics. As Christians, we don’t merely view ethics as a subject related to humanity. Ethics is about more than humans and human relationships: it’s also about the relationship between God and man.
King David writes Psalm 51 after his adultery with Bathsheba. In this psalm, David confesses to the LORD: “Against you, you only, have I sinned and done what is evil in your sight.” (v.4). He writes this after he sinned against Bathsheba (by sleeping with her) and after he killed Uriah (her husband) by commanding Joab to place him on the front lines and draw back when the fight is fiercest. David sinned against Bathsheba, he sinned against her unborn child, he sinned against Uriah, and he sinned against Joab by making him an accomplice to murder. It’s hard to think of someone David didn’t sin against. Yet, when he writes Psalm 51, he writes: “Against you, you only, have I sinned.” Why? Why does David say that he only sinned against the LORD? Is he too proud to admit that he sinned also against Bathsheba, Uriah, and Joab? No, this isn’t the case. See, David realizes something: he realizes that immorality is first and foremost a sin against God, because it’s a violation of his law and, by consequence, his holiness. David realizes that morality isn’t merely about how we should live in relation to one another, but also about how we should live in relation to God.
As Christians, we should also view morality in this way. Yes, morality is about human relations, but more significantly, it’s about the relations between God and Man. Specifically: whether Man lives according to God’s rule.
We can say, then, that the basic question of a Christian ethic is this: who is to rule the earth – God or Man?
This question is important because whoever defines ethics, he is our god. To quote Rushdoony: “It must be recognized that in any culture the source of law is the god of that society.”  This is common sense: why call Yahweh our God if we don’t live according to his law?
This would be the central distinction, then, between Christian ethics and all other ethical systems: in Christian ethics, Yahweh, the Triune God of Scripture decides morality. In all other ethical systems, autonomous Man decides morality. Even other models of theistic morality are ultimately based on the wills of men – and are only based on the will of their god (or gods) in pretense. Because any moral system that is not based on God’s revealed Word originates out of necessity from the depraved will of Man. Our Christian ethic, then, recognizes that God is King over all and that He gets to decide what’s right and wrong. Unbelieving ethics attempts to overthrow God as the ultimate foundation of morality and attempts to ground morality in the will of autonomous Man.
Van Til writes:
The Christian position maintains that man, as a creature of God, naturally would have to inquire of God what is right and wrong. Originally God spoke to man directly and man could speak to God directly. Since the entrance of sin man has to speak to God mediately. He has now to learn from Scriptures what is the acceptable will of God for him. In opposition to this the non-Christian position holds that man does not need Scripture as a final authority. And this is maintained because the non-Christian does not believe that man ever needed to be absolutely obedient to God. Non-Christian ethics maintains that it is of the nature of the ethical life that man must, in the last analysis, decide for himself what is right and what is wrong. 
Scriptural support for God’s ultimate Kingship.
God is King, and should be recognized as such by all of creation – this is the clear teaching of the Bible. Consider the following:
Sing praises to God, sing praises! Sing praises to our King, sing praises! For God is the King of all the earth; sing praises with a psalm! God reigns over the nations; God sits on his holy throne. The princes of the peoples gather as the people of the God of Abraham. For the shields of the earth belong to God; he is highly exalted!
David’s prayer in 1 Chron. 29:11-12:
Yours, O LORD, is the greatness and the power and the glory and the victory and the majesty, for all that is in the heavens and in the earth is yours. Yours is the kingdom, O LORD, and you are exalted as head above all. Both riches and honor come from you, and you rule over all. In your hand are power and might, and in your hand it is to make great and to give strength to all.
1 Chron. 29:11-12
David’s song of thanks in 1 Chron. 16:29-31:
Ascribe to the LORD the glory due his name; bring an offering and come before him! Worship the LORD in the splendor of holiness; tremble before him, all the earth; yes, the world is established; it shall never be moved. Let the heavens be glad, and let the earth rejoice, and let them say among the nations, ‘The LORD reigns!’
1 Chron. 16:29-31
Your throne, O God, is forever and ever. The scepter of your kingdom is a scepter of uprightness.
O LORD of hosts, God of Israel, enthroned above the cherubim, you are the God, you alone, of all the kingdoms of the earth; you have made heaven and earth.
God’s answer to Samuel when the Israelites demanded a king (1 Sam. 8:7):
...they have not rejected you, but they have rejected me from being king over them.
1 Sam. 8:7
In the New Testament the focus is placed on Jesus’ Kingship:
[Jesus] is the radiance of the glory of God and the exact imprint of his nature, and he upholds the universe by the word of his power. After making purification for sins, he sat down at the right hand of the Majesty on high, having become as much superior to angels as the name he has inherited is more excellent than theirs.
I charge you in the presence of God, who gives life to all things, and of Christ Jesus, who in his testimony before Pontius Pilate made the good confession, to keep the commandment unstained and free from reproach until the appearing of our Lord Jesus Christ, which he will display at the proper time—he who is the blessed and only Sovereign, the King of kings and Lord of lords, who alone has immortality, who dwells in unapproachable light, whom no one has ever seen or can see. To him be honor and eternal dominion. Amen.
1 Tim. 6:13-16
And the high priest stood up in the midst and asked Jesus, ‘Have you no answer to make? What is it that these men testify against you?’ But he remained silent and made no answer. Again the high priest asked him, ‘Are you the Christ, the Son of the Blessed?’ And Jesus said, ‘I am, and you will see the Son of Man seated at the right hand of Power, and coming with the clouds of heaven.’
Then I saw heaven opened, and behold, a white horse! The one sitting on it is called Faithful and True, and in righteousness he judges and makes war. His eyes are like a flame of fire, and on his head are many diadems, and he has a name written that no one knows but himself. He is clothed in a robe dipped in blood, and the name by which he is called is The Word of God. And the armies of heaven, arrayed in fine linen, white and pure, were following him on white horses. From his mouth comes a sharp sword with which to strike down the nations, and he will rule them with a rod of iron. He will tread the winepress of the fury of the wrath of God the Almighty. On his robe and on his thigh he has a name written, King of kings and Lord of lords.
Rev. 19:11-16 (about Jesus)
Metaethics is especially concerned with the grounding of morality. It asks not merely whether murder is immoral, but also why it’s immoral.
So what’s the foundation of Christian ethics? How do we ground our morality? Answer: We ground it in God’s will.
According to general agreement, ethics deals with that aspect of human personality which we designate as the will. This distinguishes ethics from those sciences whose primary concern it is to deal with knowledge or with appreciation … The second question that must be asked with respect to the will of man is that of criterion or standard ... Ethics seeks to discover whether the will of man is good or bad. But we cannot answer or even ask this question intelligently unless there is a standard by which a man can be judged and in comparison with which he can be said to be either good or bad. 
See, ethics deals with the human will. But the whole point of ethics is to ask what the will ought to be: what we ought to do, want, desire, hope for, work for, vote for, and kill for. But the will of man cannot be credibly judged unless there exists a standard of moral goodness independently of our will. Otherwise, if our ethics is grounded in human will, then whatever the will wants and does is right. It doesn’t make sense to ask: is it right to murder. How can it not be? By definition whatever man does is right because ethics is grounded in his will. Hence, in order to credibly consider what we ought to do, we must ground our ethics in God’s will.
What makes God’s will different from our will? Van Til explains:
As God is absolute rationality so God is also absolute will. By this we mean primarily that God did not have to become good, but has from everlasting to everlasting been good. In God there is no problem of activity and passivity. In God there is eternal accomplishment. God is finally and ultimately self-determinative. God is finally and absolutely necessary and therefore absolutely free … The basic difference, then, that distinguishes Christian from non-Christian ethics is the acceptance, or denial, of the ultimately self-determinative will of God. As Christians we hold that determinate human experience could work to no end, could work in accordance with no plan, and could not even get under way, if it were not for the existence of the absolute will of God as portrayed in Scriptures.”
To quote R.C. Sproul:
If there is no absolute Being who decrees absolute norms or absolute truth, then there is no ultimate foundation for normative ethics. And if there’s no ultimate foundation for normative ethics, then all things are permissible. Then it simply becomes a battle for convention – a battle for some people to establish their own private desires as the law for the group. 
Let me try to make all of this more tangible for you.
It can be difficult, at times, to follow what a writer means to say in such abstract a field as metaethics. Now then, we must begin by admitting that, in order to know that something is wrong (or right, for that matter), we need to know by what standard to judge it. C.S. Lewis famously pointed out that “a man does not call a line crooked unless he has some idea of a straight line.”13
But what standard should we use? Whose standard should we use? Does everyone “create” his own standard according to his subjective likes and dislikes? This doesn’t seem like a good idea, because that would mean that murderers and rapists aren’t objectively wrong when they murder and rape. After all, according to their subjective standards murdering and raping is enjoyable (and therefore: good).
So this moral standard cannot be grounded in ourselves. It needs to be grounded in something (or Someone) greater than us. This standard transcends our wills. Hence, it needs to be grounded in the will of a transcendent Being: God. He is absolutely good, and eternally so. He didn’t create goodness – He is goodness. He cannot do anything that is not good – whatever he does (even when we dislike it) is good by necessity, because God’s nature is absolutely good.
When we make moral judgments, we’re comparing ourselves and others to God’s nature. When we’re calling an action “bad,” we’re saying that it’s foreign to God: it’s something He disproves of. At the most basic level all moral judgments are comparison’s between God and man: how we measure against God’s righteous character.
Christian normative ethics.
There are two basic contentions in Christian ethics: (1) God is, (2) He’s got a law.
We get our normative ethic from God’s law. But what exactly is God’s law? Well, Jesus summarizes it pretty neatly in Matt. 22:37-40: “You shall love the Lord your God with all your heart and with all your soul and with all your mind. This is the great and first commandment. And a second is like it: You shall love your neighbor as yourself. On these two commandments depend all the Law and the Prophets.”
Notice that this is exactly the message of the Ten Commandments (Ex. 20).
The first four commandments (you shall not worship any god beside Yahweh; you shall not make – and worship – images; you shall not use the LORDS Name in vain; you shall remember the Sabbath) are about how we should live in relation to God. In simplest terms they’re about how we should love God. They can be summarized as “you shall love the Lord your God with all your heart and with all your soul and with all your mind.” (Matt. 22:37).
The last six commandments (honor your parents; you shall not murder; you shall not commit adultery; you shall not steal; you shall not lie; you shall not covet) are about how we should live in relation to one another. They’re about how we should love one another. They can be summarized as “you shall love your neighbor as yourself” (Matt. 22:39).
The underlying principle of all of Christian normative ethics is this: love towards God, and, as a consequence, love towards our neighbors.
But what is the purpose of God’s law? Why does God provide an ethical standard for us to live by? Why does He care what we do (and how we do it)? Surely He’s not threatened by our disobedience. So what is the purpose of his law?
Well, there are two purposes to God’s law: an ultimate purpose and a temporary purpose.
The ultimate purpose is for us to live in God’s presence. John writes: “This is the message we have heard from him and proclaim to you, that God is light, and in him is no darkness at all. If we say we have fellowship with him while we walk in darkness, we lie and do not practice the truth.” (1 John. 1:5-6).
In this wonderful passage, John is teaching us that God’s nature is such that He cannot be associated with unholiness. Remember we talked about how God is absolutely good? Well, imagine this Being of absolute goodness and absolute holiness associating himself with the sinful likes of us. Can He do that and remain absolutely good – absolutely holy? Can the Holy remain holy when it accepts the Unholy? No – of course not. God’s holy nature demands that we are separated from Him – that there’s no relationship between us. It is in this ultimate sense that God’s law stipulates how we ought to live if we are to be acceptable to our Lord.
But how can we ever accomplish that? How can we ever be good enough to be acceptable to God? Answer: we can’t. And this is where the temporary purpose of God’s law comes into play.
The temporary purpose of God’s law is to convict us of our unholiness, so that we may be “poor in spirit” and able to receive eternal salvation through the mediation of Jesus Christ. Either that, or that God may be justified in punishing us for our willful sins against his holiness. See, the law shows us our unholiness. When we measure ourselves against God’s perfect standard we realize how utterly depraved we really are. This realization serves as a witness: for the elect, towards salvation. For the non-elect, towards eternal damnation. John knows this, for he writes: “...and the blood of Jesus his Son cleanses us from all sin.” (1 John. 1:7). Only in Jesus can all sin be cleaned from us. Only in Jesus can we be holy.
It is of this temporary purpose that Paul writes in Rom. 7:4: “...my brothers, you also have died to the law through the body of Christ, so that you may belong to another, to him who has been raised from the dead...” Also in Gal. 2:19 he writes: “For through the law I died to the law, so that I might live to God.”
We have died to the law. But what does Paul mean by this? Does he mean that the entirety of God’s law is no longer applicable to us? This seems unlikely, for earlier in Galatians 2, Paul “opposed [Peter] to his face, because he stood condemned.” (Gal. 2:11). By what standard would Peter be condemned if the law no longer applies to the regenerate? No – Paul doesn’t mean that the entirety of God’s law no longer applies to us. He means that this temporary purpose (bringing us to Christ) is fulfilled at our rebirth. In Christ we no longer stand condemned.
How do I know that Paul is talking about the temporary purpose of the law? Well, Paul gives a reason for our dying to the law. We died to the law, he says, “in order that we may bear fruit for God.” (Rom. 7:4). The reason for our dying to the law is to bear fruit for God: to be holy. Now, being holy assumes some sort of standard of holiness. If the entirety of the law no longer applies to us, how can we be holy – or at least, by what standard ought we to be holy? In Paul’s language we could ask: what sort of fruits are we to bear if not the fruits described by the law? We don’t die to the ultimate purpose of God’s law (holiness). No, we die to the temporary purpose of God’s law (conviction of our unholiness).
Matthew Henry comments on Rom. 7:4:
Among other arguments used in the foregoing chapter to persuade us against sin, and to holiness, this was one (Rom 7:14), that we are not under the law … We are delivered from the law. What is meant by this? And how is it an argument why sin should not reign over us, and why we should walk in newness of life? We are delivered from the power of the law which curses and condemns us for the sin committed by us. The sentence of the law against us is vacated and reversed, by the death of Christ, to all true believers. The law saith, The soul that sins shall die; but we are delivered from the law. The Lord has taken away thy sin, thou shalt not die. We are redeemed from the curse of the law, Gal 3:13. 
The authority of God’s law.
Something needs to be said for the authority of God’s law in every area of life.
Let’s consider the following verses:
1 Cor. 10:31: “Whether you eat or drink, or whatever you do, do all to the glory of God.”
Col. 3:17: “Whatever you do, in word or deed, do everything in the name of the Lord Jesus, giving thanks to God the Father through him.”
Rom. 11:36: “For from him and through him and to him are all things. To him be glory forever. Amen.”
Rev. 1:8: “‘I ‘am the Alpha and the Omega,’ says the Lord God, ‘who is and who was and who is to come, the Almighty.’”
We need to ask, about the authority of God’s law, as to the scope of it’s application: is God’s law applicable only to Christians, or is it applicable to all of creation? The Biblical narrative (see the verses listed above) leaves not alternative to us, but to accept that God’s law is a truth that should be accepted by all of creation – not merely by Christians. God’s law should apply not only to our spiritual lives, but to everything we do. God’s law is true all week long – not merely on Sundays.
God’s law should also be what governs every area of society. This is a controversial statement – even among Calvinists – but it’s true. We must ask this: if God’s law is not to guide our families, churches, communities, cultures, and political considerations, what else? What’s the alternative? What will guide us if not God’s law? The only possible alternative is Man’s law – in some form or other. But what authority does Man have to decide for himself what ought to be?
The civil magistrate cannot function without some ethical guidance, without some standard of good and evil. If that standard is not to be the revealed law of God … then what will it be? In some form or expression it will have to be the law of man (or men) - the standard of self-law or autonomy. And when autonomous laws come to govern a commonwealth, the sword is certainly wielded in vain, for it represents simply the brute force of some men’s will against the will of other men … Men will either choose to be governed by God or to be ruled by tyrants. Because of the merciful, restraining work of the Holy Spirit in societies, we do not see at every stage in history these stark polarities coming to expression; most societies will to some measure strive for conformity to God’s law, even when it is officially denounced. However, in principle the choices are clearly between God’s law and man’s law, between life and death for a society. If no divine law is recognized above the law of the state, then the law of man has become absolute in men’s eyes – there is then no logical barrier to totalitarianism. 
The only alternative in principle to God’s law is Man’s law. We must ask ourselves: who would we rather be in charge – God or Man? Because if God is to be in charge (and the Bible certainly teaches that He ought to be in charge) we must accept his rule over all of creation. For what is the point to declaring God the King of all creation if we denounce the authority of his law?
The story of the seductive enemy, the wannabe-autonomous couple, and the forbidden tree.
Genesis 1 and 2 establishes God as the Creator of everything – Man included. When we read Genesis 3, then, we should keep this in the back of our minds: God is the Creator, and as such, He is to be the Determiner of what his creatures may and may not do. Though God places Man over creation (Gen. 1:28-30), Man’s rule is in no way to be ultimate: he’s expected to be the image-bearer of God – the ambassador of God. Man’s rule is not to be for himself, but for God. Man is not to be self-determinative. He is to rely on God for everything: including his ethics. Man doesn’t determine what’s right and wrong – God does.
We see this (God determining ethics) very clearly in Gen. 2:17, when God commands: “but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die.” Why does God command Man to not eat of this tree? Is it because this tree is bad-tasting or poisonous? This seems impossible for everything “was very good.” (Gen. 1:31). Why then this command? This seems arbitrary – God’s other commands are usually such that we can make sense of them: like the Ten Commandments. But what about this command? Why does God command Man to not eat of this tree?
Well, because God wants Man to acknowledge, through how he rules over creation, that God is the Determiner of right and wrong: God decides ethics. The tree’s name (“the tree of the knowledge of good and evil”) emphasizes this truth: God determines the knowledge of good and evil. God determines what man ought to do. God is to rule the earth.
We’ve all learned in Sunday School about the Fall: about Man rejecting God’s sovereign rule and choosing to rebel against God’s righteous kingship. But have you ever considered this: in eating from the tree of the knowledge of good and evil, Man wanted to determine for himself what is right and wrong. Man wanted to be the determiner of ethics. Man wanted to follow his law instead of God’s law for he wanted to “be like God, knowing good and evil.” (Gen. 3:5).
In rejecting God as King, Man not only rejects God’s rule, but also God’s law: God’s morality. Man undertakes to decide for himself what ought to be. This is the sad underlying principle of all of non-Christian ethics: that Man, in some way, determines what’s right and what’s wrong. And this is the central distinction between Christian ethics and any other ethical system: that God’s law is accepted in Christian ethics, while some version of Man’s law is exalted (and in some cases even asserted to be the law of God) in non-Christian ethics.
Who is to rule the earth – God or Man? How you answer this question will determine how you live your life. Whose law is authoritative – God’s or Man’s? Your answer will show you your god.
Will your life be founded upon the sure rock of God’s word or the ruinous sands of independent human opinion? Will your ethical decisions be crooked and inaccurate, following foolish and lawless standards, or will you wisely employ the yardstick of God’s revealed word? 
For further study.
Book: Greg Bahnsen, By This Standard.
Book (also available as video-series on YouTube): Francis Schaeffer, How Should We Then Live?
Book: Cornelius van Til, Christian Theistic Ethics.
 Greg Bahnsen, By This Standard.
 Internet Encyclopedia of Philosophy, https://iep.utm.edu/ethics/.
 Greg Bahnsen, By This Standard.
 Greg Bahnsen, By This Standard.
 Francis Schaeffer, How Should We Then Live?
 Greg Bahnsen, By This Standard.
 Douglas Wilson said this in an interview on The Remnant Radio: https://www.youtube.com/watch?v=Q23uHdaDyI8
 R.J. Rushdoony, The Institutes of Biblical Law.
 Cornelius van Til, Christian Theistic Ethics.
 Cornelius van Til, Christian Theistic Ethics.
 Cornelius van Til, Christian Theistic Ethics.
 R.C. Sproul, https://www.ligonier.org/learn/series/christian_ethics/.
 C.S. Lewis, Mere Christianity.
 Matthew Henry, Matthew Henry’s Commentary On The Holy Scriptures.
 Greg Bahnsen, By This Standard.
 Greg Bahnsen, By This Standard.