Which C.S. Lewis book was adapted from his 1941 BBC radio broadcasts?

Mere Christianity was adapted from C.S. Lewis’s 1941 BBC radio broadcasts. Lewis delivered a series of short talks during World War II that explained and defended basic Christian beliefs for a broad radio audience.

The broadcasts were later revised and collected in several stages. The first set appeared as The Case for Christianity in 1943, followed by Christian Behaviour in 1943 and Beyond Personality in 1944. These works were brought together as Mere Christianity in 1952, creating the book most readers know today.

The title does not refer to a new denomination. Lewis used “mere Christianity” for the central beliefs shared across historic Christian traditions, rather than points specific to one church. The book is therefore different from The Problem of Pain, which was published in 1940 as a focused treatment of suffering and divine goodness.