It was at this debate that many theologians say Luther's doctrine of the authority of Scripture took a bold turn. Previous to the debate, Luther prepared 13 theses. The first 12 focus on such things as indulgences, the will, and purgatory. Theses 13 though appears to come out of left field:
13. The very callous decrees of the Roman pontiffs which have appeared in the last four hundred years prove that the Roman church is superior to all others. Against them stand the history of eleven hundred years, the test of divine Scripture, and the decree of the Council of Nicaea, the most sacred of all councils.This theses takes direct aim at the supremacy of the Papacy. Luther is arguing Scripture and Nicaea do not support the infallible supremacy of Rome. Godfrey points out, "As Luther's Thesis 13 indicated, Luther initially based his argument about the papacy on tradition and on the Scripture. He argued that the Greek church had known nothing of papal primacy and that the Council of Nicaea had considered the Roman see as equal to some other sees. He also argued from 1 Corinthians 3:22f., 15:24f., and Ephesians 4 that Christ was the only head of the church" [source]. Eck countered with the oft-repeated historic claims for papal supremacy, and then cleverly argued Luther was using arguments put forth by the Hussites (Hus was a condemned by an ecumenical council as a heretic). "If Luther agreed with Hus, then he too must be a heretic" (Ibid., p. 50). Godfrey then explains,
Luther amazed the audience by boldly defending aspects of Hus's thought. He insisted again that Christ is the head of the church. He argued this point again from Scripture. It seems that at this point he really began to see the doctrine of sola scriptura. He realized that the appeals to history and tradition were uncertain. Popes and councils had made mistakes. He was beginning to see that the church needed an authority from God that is absolutely true, clear, and sufficient. As a professor of the Scriptures Luther had for some time operated with confidence in the Word of God, but he had never faced the idea that Scripture and tradition might be fundamentally at odds with one another. At Leipzig he did see the contradiction and realized that only Scripture could be the ultimate authority in the church (Ibid.).
If Godfrey is correct, it would be at Leipzig in which the formal principle of the Reformation (the doctrine of Scripture as the sufficient and ultimate authority for the church) sprang forth in Luther's theological development.
Godfrey mentions that each debater summed up the position of the other (Ibid., pp. 50-51):
Luther's view of Eck:
"I grieve that the Holy Doctor penetrates the Scriptures as profoundly as a water spider the water; in fact, he flees from them as the devil from the Cross. Therefore, with all reverance for the Fathers, I prefer the authority of the Scriptures, which I commend to the future judges."
Eck's view of Luther:
"The impatient monk is more scurrilous than becomes the gravity of a theologian. He prefers the authority of Scripture to the Fathers and sets himself up as a second Delphic oracle who alone has an understanding of the Scriptures superior to that of any Father."
Unfortunately (to my knowledge) this full debate has never been translated into English in order to check the contexts of such quotes. The good news though is Concordia plans on releasing Luther's defense of Thesis 13 against Eck at some point in the future.
One of the most intriguing aspects of the Leipzig debate is how a winner was to be determined. Erfurt and the University of Paris were to look over the record of the debate and make judgment. Erfurt didn't respond, and Paris delayed their findings until 1521. Godfrey records the fascinating decision of the Paris theologians (Ibid., pp. 51-52):
1. The Scriptures are obscure.
2. The Scriptures cannot be used by themselves.
3. The Scriptures must be interpreted by Masters, especially by the Masters of Paris.
4. The Fathers are obscure.
5. The Fathers cannot be interpreted by themselves.
6. The Fathers must be interpreted by Masters, especially by the Masters of Paris.
7. The Sentences [of Peter Lombard—the foundational medieval textbook in systematic theology] are obscure.
8. The Sentences cannot be used by themselves.
9. The Sentences must only be interpreted by Masters, especially by the Masters of Paris.
10. Therefore, the University of Paris is the chief guide in matters of Scriptural interpretation, for its decrees against Luther and Melanchthon are clear and can be understood by everyone.
Godfrey states of these points,
Luther must have smiled as he read this judgment of the Paris theologians. The Scriptures, the Fathers, and Peter Lombard are all obscure, but the contemporary theologians are clear, especially those of Paris. The pride of such a statement was stunning. But Luther must also have been amused that the Paris statement made no mention of the pope as interpreter of the truth. The theologians of Paris and various bishops of the French church had long argued a measure of independence for their church from Rome. Some of the theologians had also argued that the pope was the administrative and judicial head of the church but that he had to learn the truth that he was to enforce from the theologians. For Luther, this judgment reinforced his conviction that the church needed—and had in the Scriptures—a single, clear authority from which it knew the gospel. It confirmed the legacy of Leipzig: the Protestant doctrine of sola Scriptura (Ibid.).