From Luther's day to the present, October 31, 1517 has been considered the birthday of the Reformation. At noon on this Eve of All Saints' Day, Luther nailed on the Castle Church door, which served as a bulletin board for faculty and students of the University of Wittenberg, his Ninety-five Theses, as his Disputation on the Power and Efficacy of Indulgence has been commonly called. In the Ninety-five Theses Luther applied his evangelical theology to indulgences. He hoped thereby to find an answer to a practical problem which had disturbed him and other sincere Christians for a long time. The indulgence, or permission to relax or commute the satisfaction or penance of a contrite sinner, was a medieval development connected with the history of the sacrament of penance.
Luther's Ninety-Five Theses
Augsburg Fortress, Publishers