What is moral knowledge and how ought we use it? It helps to first understand what knowledge is. By the account of most, knowledge is a justified (or warranted) true belief. In order to have knowledge about something, I must have a justified true belief about it. Justification can take a variety of forms. For example, if I read in The New York Times that Obama was in China last week, this would be adequate justification for believing that Obama was in China. Notice that knowledge does not require certainty, it only requires that the belief is true and justified. If knowledge did require certainty, as the work of Descartes ended up showing, we could only know a very small list of things, likely just beliefs confined inside our own heads. Building the bridge to anything outside invariably introduces the possibility of being wrong, however slight, thereby precluding absolute certainty. Since Descartes, most epistemologists have realized the mistake in hankering after Cartesian certainty.

Moral knowledge, then, is a justified true belief of a moral proposition. “It is always wrong to torture children just for fun” is an example of a moral proposition.

You might wonder what kind of justification can make belief in this proposition knowledge. As Christians, we can give several different answers. One possible answer is that the proposition about torturing children for fun is “properly basic.” This means that we do not need to provide any reason to think the proposition is true in order to know that it is. A Christian can give this answer consistently by arguing that God has made humans in such a way that they simply recognize the truth of certain moral propositions immediately.

Or, alternately, we might say that justification comes from the Christian view of human persons. Since all humans, including children, are made in the image of God, they have intrinsic value and dignity. Therefore, it is always wrong to torture children for the fun of it. This is an attempt to infer wrongness from the badness of violating a person’s dignity or value. There are number of other ways we could ground our justification of this belief on the Christian view, including an appeal to God’s command to love others as we love ourselves. The bottom line is that Christianity has tremendous resources for justifying our belief in moral propositions.

What I want to suggest is that if you think Christianity is true, then you should be confident that moral knowledge is available to you. We could list a wide range of moral beliefs that a Christian should think justified, like the wrongness of adultery and stealing, the goodness and value of nature and animals, and the dignity of all human life.

Now, this robust kind of moral knowledge gives us both moral authority and responsibility. We have moral authority because we know the truth of certain moral propositions and, since we know the truth, we have an obligation to communicate that in a clear, but loving way.

As Christians, we face a problem when exercising our responsibility to tell the truth about morality: our neighbors often disagree with us about certain moral propositions. We have often been told that the greatest virtues are tolerance and humility. If there is one sin in our culture, it is the sin of speaking with authority about morality. Each person has the right to find happiness wherever and however they can, even if it means acting in ways those dogmatic Christians think disagreeable.

However, when we only practice the virtues of tolerance and humility and exclude the virtue of truth telling, then we actually harm others. If it is really true that torturing children for fun is wrong, then it is not virtuous to say to the child torturer, “Well, for me, torturing children is wrong, but you are entitled to you own opinions. You have your truth and I have mine. If it makes you happy, go ahead. If it causes you pain to stop, then don’t.” This harms the child torturer by enabling him to continue the degradation of his own soul, not to mention the harm he will continue to do to the children. Really loving the child torturer means confronting him with the truth in love.

The principle is generalizable. Consistent with regard and respect for others is the proclamation of truth. Since so many nowadays seem to identify their convictions with their very identity, challenging someone’s belief might be interpreted as something of a personal attack. This, for obvious reasons, makes expressing disagreement more challenging. Although we shouldn’t aim to be disagreeable ourselves, we should be willing to speak the truth in love, winsomely and irenically.

In The Problem of Pain, C. S. Lewis wrote about what it means for God to be good. He says,

By the goodness of God we mean nowadays almost exclusively His lovingness; and in this we may be right. And by Love, in this context, most of us mean kindness—the desire to see others than the self happy; not happy in this way or in that, but just happy. What would really satisfy us would be a God who said of anything we happened to like doing, “What does it matter so long as they are contented?” We want, in fact, not so much a Father in Heaven as a grandfather in heaven—a senile benevolence who, as they say, “liked to see young people enjoying themselves” and whose plan for the universe was simply that it might be truly said at the end of each day, “a good time was had by all”.

The point Lewis was driving at is that in order for God to be good, he cannot just leave us as we are. Real love is active and not passive. When God loves us, he helps us out of the mire of sin and depravity he found us in. He does not say, “Getting out the muck will be hard and you seem contented enough, so you stay there.” God wants us to flourish as humans and not to continue the process of rotting away. Therefore, God demands moral transformation from us. God desires what’s best for us; His love demands it.

The illumination provided by Lewis can help us think more clearly about our own responsibility to love others. If we truly love others, we will not be merely kind to them. That, in the end, is patronizing and harmful. Instead, we will call our neighbors to a life of rich happiness that is only available when we accept that we must also be holy to be happy. We must help our neighbors out of the muck and mire by telling them the truth about morality, even if they’d rather not hear it. Lucky for us, Christianity provides the grounds for doing just that.

Paul Copan and Kenneth Litwak write,

In our therapeutic age, Westerners commonly view God as a divine therapist rather than as the cosmic authority who commands our obedience and allegiance. To those who trust in him, God gives the Holy Spirit, not the Happy Spirit. God is more interested in our being good and doing good than our feeling good; he is more interested in character transformation than self-authentication. God is not only concerned about sincerity, but also that sincere hearts be aligned with the truth; after all, people can be sincerely wrong, as history amply illustrates. Only by losing our lives for Christ’s sake, by taking up our cross daily, will we actually find what is life indeed (Mt 16:25; Jn 10:10). (The Gospel in the Marketplace of Ideas, p. 55.)

The New Testament provides the earliest and most paradigmatic examples of outreach to an unbelieving world. And though the earliest evangelists were careful to be sensitive to context and to establish a solid rapport with their audiences, starting where they were, they were always true to their beliefs, had the courage of their convictions, and tried taking their listeners to where they needed to be. If this required calling sin out, identifying instances of iniquitous idolatry, calling people to repentance, and warning of the judgment to come, they were willing to do it. And so should we. The Good News of the Gospel is good news indeed, but only after people realize their malady and need for healing.