Which C.S. Lewis work was adapted from his BBC radio broadcasts about Christian belief?

C.S. Lewis’s Mere Christianity was adapted from his BBC radio broadcasts about Christian belief. The talks were delivered during the Second World War, beginning in 1941, and were later revised and collected as a book.

Lewis was invited to speak to a broad radio audience rather than only to churchgoers or academic specialists. He presented arguments about morality, human behavior, repentance, and the central beliefs shared by major Christian traditions. The broadcasts were later gathered in three parts: Broadcast Talks, Christian Behaviour, and Beyond Personality.

The book is not a detailed explanation of every denomination’s doctrines. Its purpose is to describe what Lewis regarded as “mere” or common Christianity before discussing differences among churches. The title is therefore sometimes misunderstood as meaning a casual or simplified work. In fact, it became one of Lewis’s most influential works of Christian apologetics.