In the twenty-second chapter of his De integritate (On Uprightness, 1505), a fervent plea for priests to lead blameless lives and serve as moral beacons for their parishioners, the fifty-five-year-old Jakob Wimpfeling recalled an event from his youth that changed his life. As a new student at the University of Erfurt the nineteen-year-old Wimpfeling was sitting in a church when his eyes were drawn to a motto written on the wall: "Sin not, God sees it." Wimpfeling, perhaps uneasy over his adolescent romances and the sensuous, Ovid-inspired love poems he had recently composed, was struck to the core. So searing was the message, Wimpfeling recalled, that from that time onward he dedicated himself to the pursuit of modesty, chastity, and holiness. In this pursuit he was, to a great degree, successful. He became a deeply pious, earnest, and industrious man, who, through scholarship, example, and exhortation, worked tirelessly for...