By itself, widespread criticism of the church did not lead to the dramatic changes of the sixteenth century. Instead, the personal religious struggle of a German university professor and priest, Martin Luther (1483–1546), propelled the wave of movements we now call the Reformation. Luther’s education was intended to prepare him for a legal career. Instead, however, a sense of religious calling led him to join the Augustinian friars, a religious order whose members often preached to, taught, and assisted the poor. Luther was ordained a priest in 1507 and, after additional study, earned a doctorate of theology. From 1512 until his death in 1546, he served as professor of the Scriptures at the new University of Wittenberg.

Martin Luther was a very conscientious friar, but he was plagued with anxieties about sin and his ability to meet God’s demands. Through his study of Saint Paul’s letters in the New Testament, he gradually arrived at a new understanding of Christian doctrine. His understanding is often summarized as “faith alone, grace alone, Scripture alone.” He believed that salvation and justification come through faith. Faith is a free gift of God’s grace, not the result of human effort. God’s word is revealed only in Scripture, not in the traditions of the church.

At the same time that Luther was engaged in scholarly reflections and professorial lecturing, Pope Leo X authorized the sale of a special Saint Peter’s indulgence to finance his building plans in Rome. The archbishop who controlled the area in which Wittenberg was located, Albert of Mainz, was an enthusiastic promoter of this indulgence sale.

What exactly was an indulgence? According to Catholic theology, individuals who sin could be reconciled to God by confessing their sins to a priest and by doing an assigned penance. But beginning in the twelfth century, learned theologians increasingly emphasized the idea of purgatory, a place where souls on their way to Heaven went to make further amends for their earthly sins. Both earthly penance and time in purgatory could be shortened by drawing on what was termed the “treasury of merits,” which was a collection of all the virtuous acts that Christ, the apostles, and the saints had done during their lives. An indulgence was a document signed by the pope or another church official that substituted a virtuous act from the treasury of merits for penance or time in purgatory.

Archbishop Albert’s indulgence sale, run by a Dominican friar named Johann Tetzel, promised that the purchase of indulgences would bring full forgiveness for one’s own sins or release from purgatory for a loved one. One of the slogans — “As soon as coin in coffer rings, the soul from purgatory springs” — brought phenomenal success, and people traveled from miles around to buy indulgences.

Luther was severely troubled that many people believed they had no further need for repentance once they had purchased indulgences. In 1517, he wrote a letter to Archbishop Albert on the subject and enclosed in Latin his “Ninety-five Theses on the Power of Indulgences.” His argument was that indulgences undermined the seriousness of the sacrament of penance, competed with the preaching of the Gospel, and downplayed the importance of charity in Christian life.

Luther’s “Ninety-five Theses” were quickly printed, first in Latin and then in German translation. Luther was ordered to come to Rome; because of the political situation in the empire, however, he was able instead to engage in formal scholarly debate with a representative of the church, Johann Eck, at Leipzig in 1519. He refused to take back his ideas and continued to develop his calls for reform, publicizing them in a series of pamphlets in which he moved further and further away from Catholic theology. Both popes and church councils could err, he wrote, and secular leaders should reform the church if the pope and clerical hierarchy did not. There was no distinction between clergy and laypeople, and requiring clergy to be celibate was a fruitless attempt to control a natural human drive. Luther clearly understood the power of the new medium of print, so he authorized the publication of his works.

The papacy responded with a letter condemning some of Luther’s propositions, ordering that his books be burned, and giving him two months to recant or be excommunicated. Luther retaliated by publicly burning the letter. By 1521, when the excommunication was supposed to become final, Luther’s theological issues had become interwoven with public controversies about the church’s wealth, power, and basic structure. In this highly charged atmosphere, the twenty-one-year-old emperor Charles V held his first diet (assembly of the nobility, clergy, and cities of the Holy Roman Empire) in the German city of Worms and summoned Luther to appear. Luther refused to give in to demands that he take back his ideas. His appearance at the Diet of Worms in 1521 created an even broader audience for reform ideas, and throughout central Europe other individuals began to preach and publish against the existing doctrines and practices of the church, drawing on the long tradition of calls for change as well as on Luther’s teachings.