C.S Lewis and the Devil

I suppose many of C.S. Lewis's original listeners and certainly a modern reader today reading mere Christianity might struggle with the idea of the devil. I think what Lewis is really concerned to try and bring out here is not so much the process as the outcome. The key question is what does this say about where we are, who we are right now. How does this help us understand our situation and therefore what can be done to change the human situation?