Which C.S. Lewis book was adapted from his BBC radio talks during World War II?

Mere Christianity was adapted from C.S. Lewis’s BBC radio talks during World War II. The talks were broadcast between 1941 and 1944 and aimed to explain shared Christian beliefs in accessible language.

Lewis did not initially deliver the material as a single book. The broadcasts were later revised and published in parts, then collected as Mere Christianity in 1952. The title refers to the common core of belief shared across many Christian traditions rather than to one denomination.

The work became one of Lewis’s most influential religious books. It discusses morality, human nature, Christian doctrine, and the meaning of conversion. The radio origin helps explain its direct, conversational style. Although the book is often grouped with Lewis’s apologetic works, it is distinct from The Problem of Pain, which was published earlier and addresses the problem of suffering.