The chief problem with Purgatorio is Inferno. Dante wanted to write a universal epic, like Homer's or Virgil's, but the botched and blighted souls he met in Hell were of no use. They could care less about the truth. So, in the second stage of his epic, Dante must play catch up. This he does brilliantly in the one of the most insightful depictions of the developmental psychology of sainthood since St. John Climacus. The Holy Mountain is Hell in reverse, allowing Dante to develop a system by which virtues are inculcated in the soul. The seven deadly sins are undone and the pilgrimage ends with...