From all parts of Germany letters of congratulation poured in upon Luther. Many of these came from men who had no desire for a religious change, but who thought that Luther's campaign was directed only against abuses in the Church. From the Humanists, from several of the professors and students of Wittenberg, and even from the superiors of his order he received unstinted praise and encouragement. At least one of the bishops, Lorenz von Bibra of Wurzburg, hastened to intercede for him with Frederick the Elector of Saxony, while none of the others took up an attitude of unflinching opposition. Tetzel, who had been forced to abandon his work of preaching, defended publicly at Frankfurt on the Maine a number of counter theses formulated by Conrad Wimpina. To this attack Luther replied in a sermon on indulgences in which he aimed at expressing in a popular style the kernel of the doctrine contained in his theses. Sylvester Prierias, the master of the Sacred Palace in Rome, to whom Luther's theses had been forwarded for examination, published a sharp attack upon them,[12] and was answered in Luther's most abusive style. The most distinguished, however, of the men who took the field against him was John Eck,[13] Professor of Theology and Vice-Chancellor of the University of Ingolstadt. He was a man well versed in the Scriptures and in the writings of the Fathers, a ready speaker and an incisive writer, in every way qualified to meet such a versatile opponent. While on a visit with the Bishop of Eichstatt he was consulted about Luther's theses, and gave his opinion in the Obelisks on the dangerous character of the teaching they contained. The Obelisks was prepared hastily and was not intended for publication, but it was regarded as so important that copies of it were circulated freely even before it was given to the world. Luther replied in the Asterisks , a work full of personal invective and abuse. A Dominican of Cologne, Hochstraten, also entered the lists against Luther, but his intervention did more harm than good to the cause of the Church by alienating the Humanist party whom he assailed fiercely as allies and abettors of Luther. These attacks, however, served only to give notoriety to Luther's views and to win for him the sympathy of his friends. His opponents made one great mistake. Their works were intended in great part only for the learned, while Luther aimed principally at appealing to the masses of the people. The Augustinians represented him as the victim of a Dominican conspiracy, and to show their high appreciation of his services they selected him to conduct the theological disputation at a chapter meeting held at Leipzig six months after the publication of his theses (1518). At this same meeting Luther defended the view that free will in man and all power of doing good were destroyed by original sin, and that everything meritorious accomplished by man is really done by God. His old opponent at the university, Bodenstein (surnamed Carlstadt from his place of birth), declared himself openly in favour of Luther's teaching on free will, and published a reply to Eck.

As a result of this controversy between Eck and Carlstadt it was arranged that a public disputation should be held at Leipzig (27 June- 15 July, 1519). The Catholic teaching was to be defended by Eck against his two opponents, Luther and Carlstadt. A hall in the castle of Pleissenburg was placed at the disposal of the disputants by Duke George of Saxony, who was a convinced Catholic himself, and who believed that the disputation might be the means of removing many doubts and misunderstandings. The acts of the disputation were to be drawn up and forwarded to the Universities of Paris and Erfurt for their decision. When it became known throughout Germany that a meeting had been arranged between Eck and his two principal opponents, the excitement, especially in the learned circles, became intense, and so great was the rush of scholars from all parts of the country to witness the encounter, that the immense hall was packed with an eager and attentive audience when Eck and Carlstadt entered the pulpits that had been prepared for them.