Twenty-first-century Westerners often profess an allegiance to moral relativism, stating that what is true for one person ethically may not be true for someone else. Yet, if we were to steal the wallet of a professed moral relativist, he is not going to shrug his shoulders. He will demand its return, even bringing law enforcement to bear. It turns out that even professed moral relativists expect “thou shalt not steal” to be true not only for themselves but for others. A true moral relativist would never expect other people to abide by the same law code that he does.
Consistent moral relativism—in which people live consistently by the maxim that what is true for one person may not be true for another—is virtually impossible to find. We should thank God for this, as moral relativism taken to its logical conclusions could produce only full-on anarchy in every area of society. Despite protestations to the contrary, human beings know that there is a transcendent law to which we are all accountable. Every human culture has a law code, and while these codes may differ in their specifics, there is commonality between them. For instance, all cultures prohibit the taking of innocent life. The definition of “innocent life” in one society may not match the definition in another, but there is agreement that killing is forbidden in at least some instances.
This common moral intuition is often referred to as natural law, and it is part of general revelation—those truths that God has revealed about Himself and His law in creation. The Bible is necessary to know God’s plan of salvation and for a fuller understanding of what God demands, but one does not need a Bible to have a basic knowledge of the difference between right and wrong. This law is written on the consciences of all people, and non-Christians often keep it (Rom. 2:14). They do not do so perfectly, and they lack the right motivation of glorifying God, but even those who never have seen a copy of God’s Word know they should refrain from murder, theft, and so on. This natural law, which conforms essentially to the Ten Commandments, is a restrainer of evil that allows society to function.
Natural law renders people without excuse before God (1:20). Nobody will be able to stand before the Lord on the last day and claim that they did not know what was right and wrong. In evangelism and apologetics, we can appeal to natural law in order to preach and defend the truth of God.
Our shared moral intuitions are helpful for finding a point of common ground with non-Christians as we preach the gospel. However, our moral intuitions cannot be the final arbiter of truth. Scripture alone can serve that purpose, and if a moral intuition of ours contradicts the teaching of Scripture, then we must follow Scripture. The voices of our consciences are fallible, but the Scriptures are not.