C.S. Lewis does a great job of explaining Christianity in this book. He explains hard subjects in a very down to earth way that makes sense. I would highly recommend it. The following is a quote from the book that I really liked--
"I think all Christians would agree with me if I said that though Christianity seems at first to be all about morality, all about duties and rules and guilt and virtue, yet it leads you on, out of all that, into something beyond. One has a glimpse of a country where they do not talk of those things, except perhaps as a joke. Everyone there is filled full with what we should call goodness as a mirror is filled with light. But they do not call it goodness. They do not call it anything. They are not thinking of it. They are too busy looking at the source from which it comes. But this is near the stage where the road passes over the rim of our world. No one's eyes can see very far beyond that: lots of people's eyes can see farther than mine."