Martin Luther was a Catholic monk who began to disagree with some of the Church's teachings after intensely studying the Bible. He took issue with the Church's practice of selling indulgences to forgive sins and gain favor with God, as well as the idea that salvation comes from good deeds rather than faith alone. In 1517, Luther wrote 95 theses criticizing these practices and had them nailed to the door of a church, sparking the Protestant Reformation. The Catholic Church excommunicated Luther in response, but his writings influenced many people and new Protestant denominations formed independent of Catholic authority.