structural:reformatting, quality:correction
Luther and the Ninety-five Theses

Pope Leo X (r. 1513–1521) decided to complete the construction of the new St. Peter's Basilica in Rome. As the sale of certificates of indulgences had been a well-established method of papal fund raising, he announced new indulgences in the papal bull Sacrosanctis in 1515. On the advice of the banker Jakob Fugger (d. 1525), he appointed the pluralist prelate Albert of Brandenburg (d. 1545) to supervise the sale campaign in Germany. The Dominican friar Johann Tetzel (d. 1519), a leading figure in the campaign, applied unusually aggressive marketing methods. A slogan attributed to him famously claimed that "As soon as the coin into the box rings, a soul from purgatory to heaven springs". Frederick the Wise, Prince-elector of Saxony (r. 1486–1525) forbade the campaign because the Sacrosanctis suspended the sale of previous indulgences, depriving him of revenues that he had spent on his collection of relics.

The campaign's vulgarity shocked many serious-minded believers, among them Martin Luther, a theology professor at the University of Wittenberg in Saxony. Born into a middle-class family, Luther entered an Augustinian monastery after a heavy thunderstorm dreadfully reminded him the risk of sudden death and eternal damnation, but his anxiety about his sinfulness did not abate. His studies on the works of the Late Roman theologian Augustine of Hippo (d. 430) convinced him that those whom God chose as his elect received a gift of faith independently of their acts. He first denounced the idea of justification through human efforts in his Disputatio contra scholasticam theologiam ('Disputation against Scholastic Theology') in September 1517.

On 31 October 1517, Luther addressed a letter to Albert of Brandenburg, stating that the clerics preaching the St. Peter's indulgences were deceiving the faithful, and attached his Ninety-five Theses to it. He questioned the efficacy of indulgences for the dead, although also stated " If... indulgences were preached according to the spirit and intention of the pope, all... doubts would be readily resolved". Archbishop Albert ordered the theologians at the University of Mainz to examine the document. Tetzel, and the theologians Konrad Wimpina (d. 1531) and Johann Eck (d. 1543) were the first to associate some of Luther's propositions with Hussitism. The case was soon forwarded to the Roman Curia for judgement. Pope Leo remained uninterested, and mentioned the case as "a quarrel among friars".