“Revolution” – it’s a word that conjures up images of winter palaces being stormed and the leveling of Bastilles. But if a true revolutionary is someone who regularly turns conventional thinking upside-down, then one of the world’s most prominent status-quo challengers may well be a quietly-spoken Catholic theologian who turns 85 today.

While regularly derided by his critics as “decrepit” and “out-of-touch,” Benedict XVI continues to do what he’s done since his election as pope seven years ago: which is to shake up not just the Catholic Church but also the world it’s called upon to evangelize. His...