My argument against God was that the universe seems so cruel and unjust. But how had Igotten this idea of just and unjust? A man does not call a line crooked unless he has some idea of a straight line. What was I comparing this universe with what I called it unjust? If the whole show was bad and senseless from A to Z, so to speak, why did I, who was supposed to be part of the show, find myself in such a violent reaction against it? A man feels wet when he falls into water, because man is not a water animal: a fish would not feel wet. Of course I could have given up my idea of justice by saying it was nothing but a private idea of my own. But if I did that, then my argument against God collapsed too—for the argument depended on saying that the world was really unjust, not simply that it did not happen to please my fancies. This in the very act of trying to prove that God did not exist—in other words, that the whole of reality was senseless—I found I was forced to assume that one part of reality—namely my idea of justice—was full of sense. Consequently atheism turns out to be too simple. If the whole universe has no meaning, we should never have found out that it has no meaning: just as, if there were no light in the universe and therefore no creatures with eyes, we should never know it was dark. Dark would be a word without meaning.
(C.S. Lewis, Mere Christianity, pp. 38-39)
Additional reading (article): The Faith to Doubt Christianity by Tim Keller
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