Several grim incidents increased his anxiety. While on a holiday from the university he accidentally severed an artery in his leg with his student sword. He almost bled to death and in distress prayed to the Virgin Mary for help. The death of a number of students during a plague moved him profoundly. While returning to Erfurt, following a visit to Mansfeld, he was caught in a heavy thunderstorm and a bolt of lightning struck so close that he was knocked to the ground. Overcome by panic he invoked St. Anna for aid and vowed “Help me, and I will become a monk.” Fifteen days later, on July 17, friends accompanied him to the gate of the “Black Cloister,” monastery of the Order of Augustinian Hermits in Erfurt. That this decision came later in life than usually was the case, and that his impressionable years had been spent not within the confines of a monastery but in the unrestricted atmosphere of a great university, later proved valuable to him and to the Protestant Church. Monk and Priest Luther was not received immediately into the monastery but had to remain for several months in the monastic hostelry examining himself and being examined. In September, 1505, all parties being satisfied, his head was shaved and he was invested with the black Augustinian habit and cowl, and formally received as a novice. He scrubbed the floors, begged in the streets, and engaged in various ascetic and spiritual exercises. When his probationary year was ended Luther took the vows of obedience, poverty, and chastity and was received into the order of the Augustinian monks. His sincere piety and scholarship so impressed his superiors that he was urged to prepare for the priesthood, and, on April 4, 1507, was ordained to that office. The petty employments of the monastery did not consume all of Luther’s energy and he devoted himself strenuously to studying the scholastic theology available at that time. However, long hours with books did little to ease his mind and give him the peace of conscience he sought within the cloister walls. The books taught him to rely on his own efforts to procure favor with God, and he was too honest to believe that his penitence was deep enough and his fastings worthy enough to compensate for his sins.