I am currently reading Herman Selderhuis, Martin Luther: A Spiritual Biography. I have found book repeatedly informative. I don’t know if it would be a good first biography for one to read in Luther, because it does concern itself primarily with Luther’s spiritual development.
When Luther became a doctor of theology his primary job was to teach the Bible. His teaching combined elements of the cloister and the university:
What made Luther’s teaching style unique was his combination of scholarship and devotion: he explained the Bible texts carefully using the most recent scholarly insights and then applied these to faith life. 5 During the Middle Ages, people had felt that academic theology was sterile and of little practical use. Monastic theology countered this sterility with an emphasis on the practice of a godly lifestyle. Luther’s exegesis merged these two traditions of university and monastery; this was novel but eagerly accepted by the students. It was also attributed to Luther’s success as professor that from 1515 to 1520 the number of students in Wittenberg doubled.
Luther has special Bibles printed which left spaces between the lines and had wide margins so his students could take notes (the original journaling Bible).
Luther also learned to teach the students to understand the Bible from their own reading:
Luther learned things that he in turn could also pass on to others: one becomes a theologian through oratio, meditatio, and tentatio—prayer, meditation, and trial.
For Luther, reflection was not a vague or woolly feeling about a text. Rather, it meant weighing the Word while listening in prayer, thinking deeply about the meaning of a Hebrew concept or a Greek term. According to Luther, it concerned the “rechewing” of the text8 until it opened up, as it were, and revealed the content. 9 As a result of engaging with the Word of God in this way, Luther became increasingly convinced that people have no inherent means by which they can access God. Man does not only sin; he is a sinner. Before God he stands only as a sinner, and if he denies that, then he makes God into a liar. 10 Every attempt to make oneself right before God—whether in consciousness of guilt, knowledge of sin, distress of the conscience, or remorse—is senseless. God’s grace only gets its due and honor when a person acknowledges that he or she is a sinner.lp