From Rome Luther returned to Wittenberg in the center of what today is East Germany. There he finished his studies

The Bible became very dear to Luther.

toward a doctor of theology degree. He had been advised by Staupitz, the head of the Augustinian monastery, to complete this degree and to become the chief theological professor at Wittenberg. When he received his doctorate, Luther took the Wittenberg University vow, “I swear to defend evangelical truth vigorously”—a vow which he kept throughout his life.

The Bible became very dear to Luther. As a habit he read it through once every six months.

He compared [the Bible] to a mighty tree and every word of it to little twigs, and he claimed that he had knocked on every one of these twigs to discover what they might be able to teach him.” [12]

Luther continued his lectures at Wittenberg with a wonderful series of expositions. These talks attracted students from all parts of Germany and eventually from all of Europe to the small, poor, and remote university:

He began with the Psalms, which he used to call the Bible within the Bible....He selected the Epistle to the Romans for his New Testament subject, and this led him to dwell on the thought of justification. Then came lectures on the Epistle to the Galatians. These lectures were like a revelation of the Bible to the Wittenberg students; the townspeople heard about them, aid grave burghers enrolled themselves as students in order to listen to the new and living explanations of the Word of God.” [13]

Luther realized he was weak in languages. Actually, the entire University of Wittenberg knew little of Greek and Hebrew until Melanchthon came from Erfurt to join the faculty. Luther also had few commentaries to assist him. Most of the available writings he set aside, not trusting the medieval explanations of the holy Word. He did receive help from some of those who went before. Through Augustine he received the deep impression that righteousness is based on faith, not on works. Through Bernard of Clairvaux he was enabled to love the Lord more deeply. With the help of the mystic Tauler, Luther saw clearly that anyone can have communion with God; there is no need for the intercession of a priest.

Luther insisted that the sole test of truth must be the Holy Scriptures.

Early in his career as a professor, Luther took on the responsibility of preaching in the town church of Wittenberg. Desiring that his speaking be understood by the common people, by “raw Saxons” as he called them, he followed the Lord's example of using common illustrations—such as the tilling of the ground, the sowing of seed, the sparrow, the sheep, and the fish—by collecting German proverbs and country sayings for use in his sermons.

Gradually Luther became clear concerning some basic truths: the distinction between the law and the gospel, the divine righteousness not being simply punitive justice but also being available to every believer in Christ, and faith being a trust in the living Lord rather than a belief in certain theological propositions. The following letter, which he wrote from Wittenberg, indicates some of the light he was receiving:

Learn, dear brother, Christ and Him crucified; learn to sing to Him, and doubting thyself to say to Him: “Thou, Lord Jesus, art my righteousness while I am Thy sin; what is mine Thou hast taken upon Thyself, and what is Thine Thou hast given to me.” Beware of aspiring to such purity that thou shalt no longer seem to thyself a sinner; for Christ does not dwell except in sinners....For if by our labors and afflictions we could attain peace of conscience, why did He die? Therefore, only in Him, by a believing self-despair both of thyself and of thy works, wilt thou find peace. [14]

Luther's teachings differed greatly from what was commonly taught at his time. He felt that the accepted theology was both useless and altogether untrustworthy, for it was based more on the teachings of the pagan philosopher Aristotle than on the epistles of Paul. Luther insisted that the sole test of truth must be the Holy Scriptures. The great scholastic Aquinas, however, based his Summa Theologica on Aristotle, and such teachings had the approval of the weightiest names in the medieval church. Hence, a collision was inevitable.