Which C.S. Lewis book presents Christian ideas through letters from a demon to his nephew?

The Screwtape Letters presents Christian ideas through letters from a demon to his nephew.

The Screwtape Letters was published in book form in 1942. It consists of correspondence from Screwtape, an experienced demon, to his inexperienced nephew Wormwood, who is assigned to tempt a human being known as “the Patient.” Lewis uses the fictional demonic viewpoint to satirize human weaknesses and expose methods of moral and spiritual distraction.

The unusual format lets Lewis discuss pride, envy, distraction, pleasure, suffering, prayer, and relationships without presenting the book as a conventional theological treatise. The demons’ advice is deliberately inverted: what they praise is often harmful, while what they fear is often spiritually healthy.

The work originated as a series of letters that Lewis developed after imagining the demonic perspective. It became one of his most popular Christian writings, though its satirical voice can make passages appear harsher or more literal than Lewis intended.