Screwtape is a senior devil and he is writing to his nephew, Wormwood, a junior demon with advice on how to secure the soul for their Father (the devil) of a man who has recently become a Christian. Lewis makes some penetrating insights into some of the things we are tempted with as Christians. Here is a great quote on how obedience should sometimes look for the Christian:
Do not be deceived, Wormwood. Our cause is never more in danger than when a human, no longer desiring, but still intending, to do our Enemy's will, looks round upon a universe from which every trace of Him seems to have vanished, and asks why he has been forsaken, and still obeys.