The Disputation of Leipzig:
The agreement between Militz and Luther was short-lived. Before the matter could be settled by a German bishop, it was revived by a violation of promise by both sides. A disputation between Luther and Eck was held in a large hall of the Castle of Pleissenburg at Leipzig, under the sanction of Duke George of Saxony. The debates were in Latin, but Luther broke out occasionally in his more vigorous German. The primary interest of the disputation hinged on the authority of the Pope and the infallibility of the Church. Eck maintained that the Pope is Peter’s successor and Christ’s vicar by divine right. Luther argued that this claim is contrary to Scripture, to the ancient church and to the Council of Nicaea and rests only on the decrees of Roman pontiffs. Luther concluded his argument saying, “I am sorry that the learned doctor only dips into the Scripture as the water-spider into the water - nay, that he seems to flee from it as the Devil from the Cross. I prefer, with all deference to the Fathers, the authority of the Scripture, which I herewith recommend to the arbiters of our cause."
Both parties claimed victory, but Luther was quite dissatisfied and felt that the whole event had been a waste of time. However, he had made a deep impression on many of the students at Leipzig, who soon transferred to Wittenberg. In the end, Luther always benefited more from the controversies than his enemies did.
The real importance of the debates is that it marks a progress in Luther’s liberation from the papal system. From this time on, he embarked on a ground-breaking crusade against the Roman Church until the anarchical dissentions among his own followers drove him back to a more conservation position. Nevertheless, after the Leipzig debate, Luther lost all hope of reforming the Roman Church. He was now fully prepared for a bull of excommunication.
This begins the great stormy period of his life which culminated in the Diet of Worms. Having recently learned from the book of Laurentius Valla, republished by Ulrich von Hutten, that the Donation of Constantine, by which this emperor conferred on Pope Sylvester and his successors the temporal sovereignty not only over the Lateran Palace, but also over Rome, Italy, and the whole West, was a baseless forgery of the dark ages. He therefore issued in rapid succession his three most effective reformatory works: "Address to the German Nobility," the "Babylonian Captivity of the Church," and the, "Freedom of a Christian Man."
After the Leipzig debate, Eck went to Rome and did everything possible to secure the condemnation of Luther and his followers. He was finally able to secure the bull of excommunication on June 15, 1520.