Encouraged by the dignities and the popularity which he had gained, he felt disposed, with returning health, to apply himself entirely to the study of law; and began to teach the ethics of Aristotle with other branches of philosophy. While thus engaged in secular pursuits, a singular and solemn event occurred which gave a new direction to his whole future life. One of his favorite college friends, Alexius, was cut off suddenly, and probably by the hand of violence; but the particulars of his death are uncertain: the results however were certain and important. Luther trembled. What would become of my soul, were I thus called away without warning? The terrors of death which had affected him before returned with redoubled violence and took possession of his whole soul. While in this state of mental agitation, and the solemn question of his soul's salvation still unsettled, he was overtaken by a dreadful thunderstorm near Erfurt. The lightning flashed, the thunder rolled, the terrified Luther threw himself upon the ground, imagining that the hour of death, judgment, and eternity were come. Encompassed with the terrors of death and ignorant of his way to God by the faith of Jesus, he called upon St. Anne, and made a vow that, if the Lord would deliver him from this danger, he would abandon the world, and shut himself up in a convent for the rest of his days.
The storm passed, Luther re-enters Erfurt, but not to resume his lectures, not to pursue the study of the law: his vow was upon him; he resigned his brilliant prospects for the obscurity of a cloister. This was the customary usage in those days for all who became seriously religious, in the hope of obtaining a holiness that would fit them to meet God. He knew it would greatly distress his father, and this thought pained him exceedingly, but his resolution was unalterable. About a fortnight after the event, on the 17th of August, 1505, he invited a few of his university friends to supper. As usual, music and conversation enlivened the social meeting. At an advanced hour in the evening Luther communicated his intention. This was his farewell entertainment—his farewell to the world. That same night, in spite of every remonstrance, he entered the Augustinian convent at Erfurt.
Luther could do nothing coldly or feebly. See him now leaving his friends, his books, his clothes, and in the darkness of the night hastening to the convent gate. "Open to me, in the name of God," he cried. "What do you want?" replied the friar. "To consecrate myself to God." The gate opened; Luther entered, and it closed again. He was now separated from his parents, his friends, his studies, the world; but, according to the notions of that time, his soul was now perfectly safe, he was alone with God.