The sudden change from the freedom and excitement of the university to the silence and monotony of the cloister had a depressing influence on a man like Luther, who, being of a nervous, highly-strung temperament, was inclined to pass quickly from one extreme to another. He began to be gloomy and scrupulous, and was driven at times almost to despair of his salvation; but Staupitz, the superior of the province, endeavoured to console him by impressing on him the necessity of putting his trust entirely in the merits of Christ. Yet in spite of his scruples Luther's life as a novice was a happy one. He was assiduous in the performance of his duties, attentive to the instruction of his superiors, and especially anxious to acquire a close acquaintance with the Sacred Scriptures, the reading and study of which were strongly recommended to all novices in the Augustinian order at this period.[3] In 1506 he was allowed to make his vows, and in the following year he was ordained priest. During the celebration of his first Mass he was so overcome by a sense of his own unworthiness to offer up such a pure sacrifice that he would have fled from the altar before beginning the canon had it not been for his assistants, and throughout the ceremony he was troubled lest he should commit a mortal sin by the slightest neglect of the rubrics. At the breakfast that followed, to which Luther's relatives had been invited, father and son met for the first time since Luther entered the monastery. While the young priest waxed eloquent about the happiness of his vocation and about the storm from heaven that helped him to understand himself, his father, who had kept silent throughout the repast, unable to restrain himself any longer interrupted suddenly with the remark that possibly he was deceived, and that what he took to be from God might have been the work of the devil. "I sit here," he continued, "eating and drinking but I would much prefer to be far from this spot." Luther tried to pacify him by reminding him of the godly character of monasticism, but the interruption was never forgotten by Luther himself or by his friends who heard it.

After his ordination the young monk turned his attention to theology, but, unfortunately, the theological training given to the Augustinian novices at this period was of the poorest and most meagre kind.[4] He studied little if anything of the works of the early Fathers, and never learned to appreciate Scholasticism as expounded by its greatest masters, St. Thomas or St. Bonaventure. His knowledge of Scholastic Theology was derived mainly from the works of the rebel friar William of Occam, who, in his own time, was at constant war with the Popes, and who, during the greater part of his life, if not at the moment of his death, was under sentence of excommunication from the Church. The writings of such a man, betraying as they did an almost complete unacquaintance with the Scriptures and exaggerating men's natural powers to the undervaluing or partial exclusion of Grace, exercised a baneful influence on a man of Luther's tastes and temperaments. Accepted by Luther as characteristic of Scholastic Theology, such writings prejudiced him against the entire system. Acting on the advice of the provincial, Staupitz, he gave himself up with great zeal to the study of the Bible, and later on he turned his attention to the works of St. Augustine, particularly the works written in defence of the Catholic doctrine on Grace against the Pelagians. In 1508 he went to the university of Wittenberg, founded recently by Frederick of Saxony, to lecture on Logic and Ethics, and to continue his theological studies; but for some reason, as yet unexplained, he was recalled suddenly to his monastery at Erfurt, where he acquired fame rapidly as a lecturer and preacher.