Few works of literature have had the cultural reach of John Bunyan’s The Pilgrim’s Progress.  That’s pretty amazing—who would have thought an adventure story that pauses every few pages for long discussions of Christian theology would have such a grip on the Western world’s imagination? Clearly Bunyan tapped something deep in the human spirit. The idiom of life’s journey, with all the struggles and respites along the way, is common to all mankind. One doesn’t even have to be a Christian to experience them.  When someone speaks of his “Slough of Despond” or mentions her “Celestial City,” he or she is hearkening back to one of the seminal quest stories…