Sometime during October 31, 1517, the day before the Feast of All Saints, the 33-year-old Martin Luther posted his 95 Theses on the door of the Castle Church in Wittenberg.

The door functioned as a bulletin board for various announcements related to academic and church affairs. Luther was calling for a “disputation on the power and efficacy of indulgences out of love and zeal for truth and the desire to bring it to light.” He did so as a faithful monk and priest who had been appointed professor of biblical theology at the University of Wittenberg, a small, virtually unknown institution in a small town.

Luther was calling for a debate on a pressing issue: the relationship between money and religion. “Indulgences” had become the complex instruments for granting forgiveness of sins. The granting of forgiveness in the sacrament of penance was used to discipline sinners. Penitent sinners were asked to show regret for their sins (contrition), confess them to a priest (confession), and do penitential work to atone for them (satisfaction).

Indulgences were meant to relax or commute the penitent sinner’s work of satisfaction. By the late eleventh century it had become customary to issue indulgences to volunteers taking part in the Crusades. All sins would be forgiven anyone participating in such a dangerous but holy enterprise.

As the years passed the sale of indulgences was used to build cathedrals and for political purposes. Luther was committed to the idea that salvation could be reached through faith and by divine grace only, and vigorously objected to the corrupt practice of selling indulgences. It was the abuse of this practice that inspired Martin Luther to start a dialogue.

The “Disputation on the Power and Efficacy of Indulgences,” also known as “The 95 Theses,” was a list of questions and propositions for debate. Popular legend has it that on October 31, 1517 Luther defiantly nailed a copy of his 95 Theses to the door of the Wittenberg Castle church. The reality was probably not so dramatic; Luther more likely hung the document on the door of the church matter-of-factly to announce the ensuing academic discussion around it that he was organizing.

The 95 Theses, which would later become the foundation of the Protestant Reformation, were written in a remarkably humble and academic tone, questioning rather than accusing. The overall thrust of the document was nonetheless quite provocative. The first two of the theses contained Luther’s central idea, that God intended believers to seek repentance and that faith alone, and not deeds, would lead to salvation. The other 93 theses, a number of them directly criticizing the practice of indulgences, supported these first two.

Martin Luther is one of the most influential figures in Western history. His writings were responsible for sparking the Protestant Reformation. His central teachings, that the Bible is the central source of religious authority and that salvation is reached through faith and not deeds, shaped the core of Protestantism.