It seems impolite to say so, given Pope Benedict XVI’s chastened retreat to the shadows of the Vatican, back in 2013, but his papacy was a failed one. For nearly eight years, he led the Catholic Church in the broad collapse of its moral authority, from the crisis of criminal priests to the further alienation of women to the blatant dysfunction of the Church’s own bureaucracy. Still, there is one sense in which Benedict succeeded. After a career spent railing against relativism, he relativized the world’s last divine-right office, becoming the first Pope since 1415 to resign and giving his successor, Francis, the sway that he so astonishingly exploits today. At the end, the self-styled Pope Emeritus, still dressed in his white robes, lifted off from the Vatican in a white helicopter, which took him to Castel Gandolfo, the papal vacation palace on a lake outside Rome. He assumed the quiet, cloistered existence of a retired prelate. Today, he has broken his silence with “Last Testament,” a late-in-life attempt at personal reckoning that amounts, instead, to a reiteration of the ethical detachment that undercut him from the start.