What was the original title of C.S. Lewis’s book based on his wartime radio talks?

C.S. Lewis’s book based on his wartime radio talks was titled Mere Christianity.

Lewis delivered a series of Christian talks for the BBC during the Second World War, beginning in 1941. He later revised and expanded the material into books, which were collected as Mere Christianity. The final title refers to the shared core of Christian belief rather than to one denomination.

The work is divided into broad sections commonly titled “Right and Wrong as a Clue to the Meaning of the Universe,” “What Christians Believe,” and “Christian Behaviour.” Lewis’s broadcast voice made him widely known in Britain, while the book later became one of his most influential works of popular Christian apologetics.