Heiko A. Oberman, Luther: Man Between God and the Devil (Doubleday, 1989) 138-140.
Since the summer semester of 1507 [Luther] had been devoting himself to the study of theology under the guidance of Johannes Nathin, the senior Brother, who held the Augustinian chair of theology at the University of Erfurt. Despite intensive research, nothing of significance has as yet been discovered about this theologian who must have been a real influence on Luther in Erfurt. Have all his writings disappeared, or did he really never publish anything? All we know is that he received his master’s degree in Erfurt thirty years before Luther was enrolled there and that he spent four to five years in Tübingen as a younger colleague of Gabriel Biel, holding survey lectures on the whole range of theological fields.
Luther thoroughly prepared himself for his first mass with the help of Biel’s comprehensive exposition of the canon of the mass, published in 1488. Now, as a student at the theological faculty, he was introduced by Nathin to the best theological textbook of the time, Biel’s dogmatics, which was also a survey of the history of Christian thought. The renowned nominalist from Tübingen had, in the traditional medieval manner, laid out his voluminous tome as a commentary on the scholastic theological textbook know as the Sentences of Peter Lombard. Philipp [sic] Melanchthon later related that Luther had studied his Biel so intensively that the Reformer was able to quote whole pages from memory. How assiduously he pored over Biel’s commentaries can still be seen from the critical comments he wrote in the margins of his own copy in earlier and later years. Even when Luther was already distancing himself from theology as he had been taught it, he still recommended Biel as a fine guide for priests hearing confession.
In April 1508 the budding theologian was already listed as a lecturer of his order next to such experience Doctors as Paltz and Nathin. It is unlikely that Luther had much personal contact with his senior colleague Johannes von Paltz. Though still an official member of the monestary, Paltz, after a clash with his brethren, left Erfurt in a huff in 1505 to become the prior of the monastery at Mühlheim near Koblenz. Despite his physical absence Paltz was very much present through his widely read writings, which were characterized by a readily understandable, colorful type of medieval piety. He was the spokesman for the monks, extolling the monastic way of life as the sure way to salvation.
But Johannes von Staupitz had already turned his attention to Luther. Not only did he encourage the young, striving monk theologically and spiritually, he also involved him in the turmoil of his daring Augustinian politics. Luther became a wanderer between two monastic factions – even literally so during the years before he obtained his doctoral degree in theology. First Staupitz summoned the Augustinian lecturer from Erfurt to Wittenberg for the winter semester of 1508-09 to lecture on Aristotle’s Ethics, and instructed him to prepare for his doctorate in theology at the same time. In the autumn of 1509 Nathin, undoubtedly having discussed the matter with Staupitz, recalled Luther to Erfurt…After rendering one and three-quarters years of service to his home monastery as a member of the theological faculty in Erfurt he was recalled by Staupitz to Wittenberg.