If we have missed C. S. Lewis' message so far, he makes it quite clear as he closes out Chapter 1. His words are not difficult so I put them forth as he wrote his summation.
First, that human beings all over the earth have this curious idea that they ought to behave in a certain way, and cannot really get rid of this idea.
Second, that we do not in fact behave this way. We know the Law of Human Nature and we break it.
These two facts are the foundation of all clear thinking about ourselves and the universe we live in.
Does the reality of the Law of Human Nature (Right and Wrong) have anything to do with Jesus? Does the existence of this Law change anything about what Jesus did when He was on earth. Does it change anything about your faith or lack of faith in Jesus?