What book grew from C.S. Lewis’s BBC radio talks on Christian belief?

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

Lewis aimed to present a shared core of Christian belief rather than defend one particular denomination. The book is organized into sections on right and wrong as a clue to the meaning of the universe, Christian beliefs, Christian behavior, and the doctrine of the Trinity.

The title does not mean a minimal or casual form of Christianity. “Mere Christianity” refers to what Lewis regarded as common ground among historic Christian traditions. The Problem of Pain is a separate book from 1940, while Miracles was first published in book form in 1947.