Which C.S. Lewis book collects radio talks later adapted into a Christian apologetics work?

Mere Christianity collects C.S. Lewis’s radio talks and presents them as a Christian apologetics work.

Lewis delivered the original broadcasts for the BBC during the Second World War. The talks were broadcast in three series between 1941 and 1944, beginning with “Right and Wrong: A Clue to the Meaning of the Universe.” Lewis later revised and combined the material into the book Mere Christianity, published in 1952.

The title refers to what Lewis regarded as the shared core of historic Christianity rather than the distinctive teachings of a particular denomination. The book discusses morality, belief, Christian doctrines, and the development of Christian character. Its conversational style helped make complex religious arguments accessible to a broad radio audience.

Mere Christianity is not a transcript of one uninterrupted broadcast series. It incorporates material from several sets of talks and includes revisions made for print. The work is also distinct from The Problem of Pain, which Lewis published in 1940 as a focused treatment of suffering and divine goodness.