The Wikipedia article of the day for October 31, 2017 is Ninety-five Theses.
The Ninety-five Theses are a list of propositions written by Martin Luther that started the Protestant Reformation, a schism in the Catholic Church. Luther, a professor of moral theology at the University of Wittenberg, Germany, enclosed them in a letter to the Archbishop of Mainz on 31 October 1517, a date now commemorated annually as Reformation Day. They advance Luther’s positions against the selling of plenary indulgences, certificates that were said to reduce the punishment for sins in purgatory. Luther claimed that his positions accorded with those of the pope, but the Theses contradict a 14th-century papal bull. Luther’s ecclesiastical superiors had him tried for heresy, which culminated in his excommunication in 1521. Though the Theses mark the start of the Reformation, Luther did not consider indulgences to be as important as other theological matters which would divide the church, such as justification by faith and the bondage of the will. His breakthrough on these issues would come later, and he did not see the writing of the Theses as the point at which his beliefs diverged from those of Rome.