Which work by C.S. Lewis explains Christianity through a series of broadcast talks?

Mere Christianity is the C.S. Lewis work that developed from a series of broadcast talks explaining Christian belief. The talks were delivered for the BBC during the Second World War and later revised into book form.

Lewis first presented the material in radio broadcasts beginning in 1941. He aimed to explain what he described as common or shared Christian beliefs rather than defend one particular denomination. The talks reached a large audience during a period when public communication about religion had a prominent role in Britain.

The book was published in stages before appearing in its familiar collected form. Its sections discuss moral law, Christian beliefs, and Christian conduct. Lewis used arguments, analogies, and ordinary language rather than writing as a technical theologian.

Mere Christianity is sometimes confused with The Problem of Pain, another Lewis book about Christian belief. The Problem of Pain is a separate work published in 1940. The broadcast origin is the identifying clue: the radio talks became Mere Christianity.