As he was returning to Erfurt from a visit home, he was overtaken by a terrific thunderstorm, in which his excited imagination saw a devine warning to forsake the "world." In a fright he vowed to St.Ann to become a monk and, though he at once regretted the rash promise, on July 17, 1505, he discharged it by entering the Augustinian friary at Erfurt.

After a year's novitiate he took the irrevocable vows of poverty, chastity, and obedience.

In 1507 he was ordained priest.

In the winter of 1510-1 he was sent to Rome on business of the order, and there saw much of the splendor and also of the corruption of the capital of Christendom.

Having started, in 1508, to teach Aristotle at the recently founded University of Wittenberg, a year later he returned to Erfurt, but was again called to Wittenberg to lecture on the Bible, a position he held all his life.