Lewis declines to say how he obtained the letters that follow but warns readers neither to discount the existence of devils nor interest themselves in them excessively. He also provides guidance for interpreting the text: “[R]emember that the devil is a liar” (ix). This applies particularly to the characters in the narrative, who may not be described accurately.

The senior devil Screwtape writes to his nephew Wormwood, who is a novice tempter. Wormwood has been given the assignment to manipulate a young man, his “patient,” and win him over to the devil’s camp. Wormwood has sought to do this by encouraging the patient to spend time with agnostics or atheists, but Screwtape considers his approach ham-fisted; in the modern era, Screwtape claims, people are less convinced by reason than by emotion, so Wormwood should try to make the patient consider materialism “courageous” rather than “true.” He further advises encouraging the patient to focus his attention on the “stream of immediate sense experiences” and to avoid “universal issues” (2), even if the latter seem superficially opposed to religious belief. An emphasis on philosophy and logic might lead the patient to think about and be attracted to religious thoughts and connections with the divine.