Which C.S. Lewis book explains Christianity through a series of imagined wartime radio talks?

Mere Christianity explains Christianity through a series of imagined wartime radio talks. C.S. Lewis originally delivered the talks for the BBC during the Second World War, beginning in 1941.

The broadcasts were later revised and collected into a book titled Mere Christianity. Lewis presents what he calls “mere Christianity”: core beliefs shared across historic Christian traditions, rather than the distinctive teachings of one denomination. The work discusses morality, belief, Christian doctrine, and the practical meaning of faith.

The book is divided into sections that originated in different broadcast series. Broadcast listeners knew the talks under titles such as “The Case for Christianity” and “Christian Behaviour,” while the later book gave them a unified structure.

Mere Christianity is not a novel and does not narrate the history of Lewis’s conversion. It is an apologetic work, meaning that it offers reasoned arguments in defense or explanation of religious belief.