Tetzel preached with considerable success in Halberstadt, Magdeburg and Leipzig, and in May 1517 he found himself in the neighbourhood of Wittenberg, whence many people flocked to see him, and to gain the Indulgence. This was not calculated to please Luther or his patron the Elector, Frederick of Saxony, and provided Luther with an occasion of giving vent to his own views on good works, Grace, and Justification. Years before, both in his sermons attacking the Augustinians of the strict observance for their over confidence in the merits of good works and penance, and in his commentaries on the Epistles of St. Paul to the Romans and to the Galatians, he had indicated already that his views on man's power to do anything good, and on the means and nature of justification differed widely from those put forward by Catholic theologians. At last, after careful consideration, following the bent of his own inclination and the advice of his friends, he determined to take the field openly by publishing, on the eve of the festival of All Saints, 1517, his celebrated seventy theses against Indulgences.[10] This document was drawn up with great skill and foresight. Some of the theses were perfectly orthodox and professed great reverence for the teaching of the Church and the authority of the Pope; others of them were open to an orthodox as well as to an unorthodox interpretation; others, still, were opposed clearly and definitely to Catholic doctrine, and all of them were put forward in a way that was likely to arrest public attention and to win the support of the masses.[11] They were affixed to the doors of the university church in Wittenberg, and copies of them were spread broadcast through Germany. Before a week had elapsed they were discussed with eagerness in all parts of the country, and the state of feeling became so intense that Tetzel was obliged to discontinue his mission, and to retire to Frankfurt, where under the direction of Wimpina, he set himself to draw up a number of counter theses which he offered to defend.

The circumstances of the time were very favourable to a campaign such as Luther had initiated. The princes of Germany and even some of the bishops made no secret of their opinion that indulgences had been abused, and many of them were anything but displeased at the step that had been taken by the Wittenberg professor. The old opposition between the Teuton and the Latin was growing daily more marked owing to the violent and abusive language of men like Ulrich von Hutten, who posed as German patriots; while the Humanist party, roused by the attacks made upon Reuchlin by the Dominicans of Cologne, backed by the Scholastic Theologians, were not sorry to see their opponents challenged in their own special department, and obliged to act on the defensive. The knights or lower nobles, too, who had been deprived of many of their privileges by the princes, were ready for any scheme of violence in the hope that it might conduce to their advantage; and the lower classes ground down for centuries were beginning to realise their own strength, partly owing to the spread of secret societies, and were willing to lend a ready ear to a leader who had given expression to views that were coursing already through their minds.