The sixteenth-century document that changed the course of Christianity. Monk and theology professor Martin Luther found himself in disagreement with the Roman Catholic Church on the subject of indulgences—certificates sold by the Church that promised to spare their owners from punishment for their sins. With his 95 Theses , Luther proposed a debate on the subject, but ultimately, he was excommunicated and the Protestant Reformation began. This is both a religious document and a historical one—a turning point that marked a challenge to papal authority, set off political conflicts and bloody war in Europe, and led to the remarkable variety of Christian denominations and sects that exist in the world today.