Which C.S. Lewis book was published in 1940 as a defense of Christianity?

The Problem of Pain was published in 1940 as C.S. Lewis’s defense of Christianity.

The Problem of Pain examines why suffering exists if God is good and powerful. Lewis discusses subjects including divine omnipotence, human freedom, the Fall, animal pain, and hell. The book presents a philosophical and theological argument rather than a personal diary of bereavement.

Lewis wrote it before the deaths and personal losses that later shaped A Grief Observed. That distinction matters because readers sometimes treat the two books as if they addressed pain from the same standpoint. The Problem of Pain is primarily an apologetic work; A Grief Observed records the experience of mourning.

The book helped establish Lewis as a prominent Christian apologist. Its title identifies the central issue directly: the intellectual and theological difficulty posed by suffering.