Same article:
Marty writes that Luther sought assurances about life, and was drawn to theology and philosophy, expressing particular interest in Aristotle, William of Ockham, and Gabriel Biel.[17] He was deeply influenced by two tutors, Bartholomäus Arnoldi von Usingen and Jodocus Trutfetter, who taught him to be suspicious of even the greatest thinkers,[17] and to test everything himself by experience.[18] Philosophy proved to be unsatisfying, offering assurance about the use of reason, but none about the importance, for Luther, of loving God. Reason could not lead men to God, he felt, and he developed what Marty describes as a love-hate relationship with Aristotle over the latter’s emphasis on reason.[18] For Luther, reason could be used to question men and institutions, but not God. Human beings could learn about God only through divine revelation, he believed, and Scripture therefore became increasingly important to him.[18]
He decided to leave his studies and become a monk, later attributing his decision to an experience during a thunderstorm on July 2, 1505. A lightning bolt struck near him as he was returning to university after a trip home. Later telling his father he was terrified of death and divine judgment, he cried out, “Help! Saint Anna, I will become a monk!”[19] He came to view his cry for help as a vow he could never break.
He left law school, sold his books, and entered a closed Augustinian monastery in Erfurt on July 17, 1505.[20] One friend blamed the decision on Luther’s sadness over the deaths of two friends. Luther himself seemed saddened by the move, telling those who attended a farewell supper then walked him to the door of the Black Cloister, “This day you see me, and then, not ever again.”[18] His father was furious over what he saw as a waste of Luther’s education.[21]