Which C.S. Lewis book presents Christianity through radio talks later collected in print?

Mere Christianity presents Christianity through radio talks later collected in print.

The material began as a series of BBC radio broadcasts delivered by C.S. Lewis during World War II. The talks were intended for a broad audience and explained basic Christian beliefs in accessible language rather than focusing on the distinctive doctrines of one denomination.

Lewis revised and expanded the broadcasts into three sections: Broadcast Talks, Christian Behaviour, and Beyond Personality. The combined book was published in 1952. Its title refers to the shared core of Christian belief, not to a separate church or denomination.

A famous part of the work is Lewis’s argument that Jesus cannot be treated merely as a great moral teacher if the claims attributed to him are taken seriously. The book also discusses morality, charity, marriage, and the Trinity. It remains one of Lewis’s most widely read works of Christian apologetics.