C. S. Lewis opens his famed book, Mere Christianity, by presenting a convincing case for the existence of God. I am going to summarize his argument here; but I recommend you purchase the book and read it for yourself—it’s an easy-to-read classic.
Lewis begins with a description of people arguing over some misdeed that has been committed. Cutting in line. Stealing a seat. Breaking a promise. He notes how fascinating it is that people always make the claim that the offending deed was wrong. Even if they don’t make that claim outright, the fact that they are so upset indicates that they believe some rule has been broken. Moreover, the offender hardly ever says, “To hell with your standard” (Lewis’ words). Instead, he explains why his actions were justified—he had some special reason for breaking the rule. This, of course, admits that there is in fact a standard. And if the offender is so bold as to claim that there is no standard—that he can do whatever he wants—he almost always appeals to this very standard when someone wrongs him later on!
Lewis then claims something bold. The above scenario indicates that there is indeed a basic universal standard of morality governing all humans. Sure, different civilizations have had slightly different perspectives about how morality should play out; but there have never been any major differences between societies regarding basic morality (a point further defended as Lewis continues). But the astounding thing is this: though we all sense obligation to this Moral Law, none of us really keep it! Over time “we have all failed to practise ourselves the kind of behaviour we expect from other people.” And when we do fail to practice it, we almost always make excuses for why our failure is understandable, given the circumstance. Of course, this just further proves how real the Moral Law is to us and how obligated we feel to keep it.
If there is a Moral Law, there must be a Lawgiver. God is the best explanation for the fact that all humans have, more or less, this concept of right and wrong.
If you find any of this compelling, or if you have some objections to Lewis’ logic (or rather my imperfect summary of it), please watch this video. It is a reading of a chapter from Mere Christianity in which Lewis tackles some of the major objections to his claim.