For those unfamiliar, Screwtape is a middle-class demon who has written letters of instruction to Wormwood (his underling) in the art of deception and manipulation of his "human" to prevent his acceptance of Christ as his Savior and - if that horror of horrors occurs - to continuously attack him to minimize his effectiveness as a soldier of God. Through the letters, we learn many things - perhaps the most important is this: If we deceive ourselves that either demons don't exist at all OR that they exist and we are helpless to their manipulations, we are playing right into the hands of their evil intent. Not only must we balance our understanding that demons DO exist (Jesus, Himself, spoke with them and expelled them from inhabiting men) and we can be influenced by them in a seemingly multitude of distracting to disturbing manners, but also that, once indwelt with the Holy Spirit, we have the power of God to protect us. In fact, Satan is not the negative corrolary of God, but the evil counterpart to angels such as Michael (revisit the description of the fallen "angel"). God's power is infinitely greater than Satan's. All of Satan's power here on earth is only with permission of God in the effort to truly turn our free-willed souls to Christ. Excellent book, highly recommended. Also, Alcorn's "Lord Foulgrin's Letters" is a modern version along the same lines with the same convicting results.