What was C.S. Lewis’s first published book of Christian apologetics?

C.S. Lewis’s first published book of Christian apologetics was The Problem of Pain.

Published in 1940, The Problem of Pain examines why suffering exists if God is both good and powerful. Lewis discusses human freedom, divine goodness, pain, hell, animal suffering, and the Christian understanding of the Fall. It was written as a theological and philosophical argument rather than as a personal memoir.

The book appeared after Lewis had returned to Christianity and had become a prominent public speaker on religious questions during the Second World War. Its arguments helped establish his reputation as a popular Christian apologist, although the book addresses suffering in a more abstract way than some of his later writings.

Mere Christianity is often mistaken for his first apologetic book because it became his best-known work in the field. However, Mere Christianity was assembled from wartime radio broadcasts and published in book form beginning in 1952. The Problem of Pain predates it by twelve years.