Which 1933 book was C.S. Lewis's first published work of Christian fiction?

The Pilgrim’s Regress was C.S. Lewis’s first published work of Christian fiction.

Published in 1933, the book is an allegorical fantasy subtitled An Allegorical Apology for Christianity, Reason and Romanticism. Its central character, John, travels through a landscape filled with symbolic figures and obstacles while seeking the source of a troubling desire.

The title deliberately echoes John Bunyan’s The Pilgrim’s Progress, the famous seventeenth-century Christian allegory. Lewis’s version reflects his own intellectual and spiritual concerns, including his movement from atheism to Christianity and his interest in the relationship between reason, imagination, and longing.

The Screwtape Letters appeared in 1942, The Great Divorce in 1945, and Till We Have Faces in 1956. Those books are also fictional works with Christian themes, but they were published later and do not hold the distinction of being Lewis’s first Christian fiction.