"A young man who wishes to remain a sound atheist cannot be too careful of his reading," wrote C.S. Lewis. That's probably true, especially because the young man might read Lewis's own Mere Christianity, a book that has proven so influential it now has its own "biographer" in George M. Marsden, author of C.S. Lewis's Mere Christianity: A Biography.

In a 10-minute conversation with The Bookmonger, Mardsen explains how Lewis turned a set of radio broadcasts into an enduring work of apologetics, what made Lewis such a good writer, and why Mere Christianity is more popular today than ever before.