Which C.S. Lewis book adapts his BBC broadcasts about basic Christian belief?

Mere Christianity adapts C.S. Lewis’s BBC broadcasts about basic Christian belief. The broadcasts began during World War II, and Lewis presented them in language intended for a broad radio audience rather than only for theologians.

The material was later revised and published in book form. Lewis arranged it around shared Christian ideas, including morality, belief, and the Christian understanding of Jesus. The title refers to what Lewis regarded as common or central Christianity, not to a separate denomination.

The book is sometimes mistaken for The Problem of Pain because both are major works of Lewis’s religious writing. The Problem of Pain focuses especially on the intellectual and theological problem of suffering. Mere Christianity instead grew directly from a sequence of radio talks and became one of Lewis’s most widely read nonfiction works.