Which C.S. Lewis book presents Christianity through radio broadcasts later adapted into chapters?

Mere Christianity presents Christianity through radio broadcasts later adapted into chapters.

Lewis delivered the original talks for the BBC during the Second World War. The first series, Broadcast Talks, aired in 1942, followed by Christian Behaviour in 1943 and Beyond Personality in 1944. Lewis revised and combined this material into the book Mere Christianity, published in 1952.

The work explains core Christian beliefs rather than defending one particular denomination. Lewis discusses moral law, human behavior, Christian doctrine, and the significance of the Christian understanding of Jesus. The title refers to what Lewis regarded as the common or central beliefs shared by historic Christian traditions.

The book is sometimes described as a transcript of a single radio series, but it actually grew from several sets of broadcasts and was substantially revised for publication. It also differs from The Problem of Pain, which is a separate 1940 book focused on suffering and the problem of evil.