What was the title of C.S. Lewis’s first book about Christianity after his conversion?

C.S. Lewis’s first book about Christianity after his conversion was The Pilgrim’s Regress.

Published in 1933, The Pilgrim’s Regress was Lewis’s first published work after his return to Christian belief. Its subtitle, An Allegorical Apology for Christianity, Reason and Romanticism, signals its allegorical structure. The story follows John as he searches for a distant island, encountering figures and ideas that represent intellectual and spiritual positions.

Lewis had converted to Christianity in stages during the late 1920s and early 1930s. The book reflects his personal intellectual journey, including his movement from atheism toward theism and then Christianity. Its style is more allusive and demanding than the later broadcast talks that became Mere Christianity.

The title deliberately echoes John Bunyan’s The Pilgrim’s Progress, but Lewis’s book is not a sequel. The two works share an allegorical journey structure while presenting different characters, arguments, and historical contexts.