The Screwtape Letters is about devils trying to sway a man's soul into hell. The back of the book said it was satirical and funny but I didn't find it terribly amusing, I think that's what 50 years or so does to literature. It was interesting thought, because the devils weren't trying to get the man to do things you'd normally think they'd like. They're not trying to make him murder his friends or beat up kids or steal bread. They're trying to bring him down with the monotony of life, make him think everything is absurd and unworthy of being appreciated. They don't want him to love anyone. They don't want him to make friends who help him find joy in life, they want him to make friends with the "right" people in society. In one place in the book they talk about how their real goal is just to have the guy sitting alone in a room as night falls, watching the fire die down. Bored, alone, thinking that life is completely trivial.
The devils also want the man to lose himself, to think he's a meaningless part of society. They say that God wants us to acknowledge our gifts and be the individuals we were created to be, as Christians we are more "ourselves" than if we are out of touch with our creator. To separate the man from God and joy they put ideas into the man's head... make him afraid of pride so he can't enjoy what he has to offer, confuse him with what sins are worse than others. Be a distraction.
Anyway, this wasn't my favorite C.S. Lewis book but it gave me some good points to think about. I'd still recommend it, especially to a Christian who's wondering where the fun and joy and adventure are in life after religion.