Advice on reading Lewis and other Christian writings

I want to start by saying something that I would like every one to notice carefully. It is this. If this chapter means nothing to you, if it seems to be trying to answer questions you never asked, drop it at once. Do not bother about it at all. There are certain things in Christianity that can be understood from the outside, before you have become a Christian. But there are a great many things that cannot be understood until after you
have gone a certain distance along the Christian road. These things are purely practical, though they do not look as if they were. They are directions for dealing with particular crossroads and obstacles on the journey and they do not make sense until a man has reached those places. Whenever you find any statement in Christian writings which you can make nothing of, do not worry. Leave it alone. There will come a day, perhaps years later, when you suddenly see what it meant. If one could understand it now, it would only do one harm.
C.S. Lewis, Mere Christianity (1952; Harper Collins 2001) 144.