[b] The Theses is retrospectively considered to have launched the Protestant Reformation and the birth of Protestantism, despite various proto-Protestant groups having existed previously.

Though the Theses were 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 alone and the bondage of the will.

Martin Luther, professor of moral theology at the University of Wittenberg and town preacher,[3] wrote the Ninety-five Theses against the contemporary practice of the church with respect to indulgences.

[6] Popes are empowered to grant plenary indulgences, which provide complete satisfaction for any remaining temporal punishment due to sins, and these were purchased on behalf of people believed to be in purgatory.

Rulers often sought to receive a portion of the proceeds or prohibited indulgences altogether, as Duke George did in Luther's Electoral Saxony.

[10] In 1515, Pope Leo X granted a plenary indulgence intended to finance the construction of St. Peter's Basilica in Roma.

[16] Luther became especially concerned in 1517 when his parishioners, returning from purchasing Tetzel's indulgences, claimed that they no longer needed to repent and change their lives in order to be forgiven of sin.

After hearing what Tetzel had said about indulgences in his sermons, Luther began to study the issue more carefully, and contacted experts on the subject.

[21] The first thesis states, "When our Lord and Master Jesus Christ said, 'Repent,' he willed the entire life of believers to be one of repentance."

In the first few theses Luther develops the idea of repentance as the Christian's inner struggle with sin rather than the external system of sacramental confession.

[22] Theses 5–7 then state that the pope who Luther called the Vicar of Christ on earth can only release people from the punishments he has administered himself or through the church's system of penance, not the guilt of sin.

Theses 14–16 discuss the idea that the punishment of purgatory can be likened to the fear and despair felt by dying people.

He sees it as encouraging sinful greed, and says it is impossible to be certain because only God has ultimate power in forgiving punishments in purgatory.

[25] Theses 30–34 deal with the false certainty Luther believed the indulgence preachers offered Christians.

Luther also mentions the question of why the pope, who is very rich, requires money from poor believers to build St. Peter's Basilica.

Luther claims that ignoring these questions risks allowing people to ridicule the pope.

[31] Luther closes the Theses by exhorting Christians to imitate Christ even if it brings pain and suffering.

Karlstadt posted his theses at a time when the relics of the church were placed on display, and this may have been considered a provocative gesture.

[36] Luther's theses were intended to begin a debate among academics, not a popular revolution,[35] but there are indications that he saw his action as prophetic and significant.

In the letter, Luther addresses the archbishop out of a loyal desire to alert him to the pastoral problems created by the indulgence sermons.

[40] No copies of a Wittenberg printing of the Ninety-five Theses have survived, but this is not surprising as Luther was not famous and the importance of the document was not recognized.

[49] In February 1518, Pope Leo asked the head of the Augustinian Hermits, Luther's religious order, to convince him to stop spreading his ideas about indulgences.

[60][g] Another prominent opponent of the Theses was Johann Eck, Luther's friend and a theologian at the University of Ingolstadt.

[58] Luther was summoned by authority of the pope to defend himself against charges of heresy before Thomas Cajetan at Augsburg in October 1518.

[66] The indulgence controversy set off by the Theses was the beginning of the Reformation, a schism in the Roman Catholic Church which initiated profound and lasting social and political change in Europe.

[68] The Theses also made evident that Luther believed the church was not preaching properly and that this put the laity in serious danger.

[70] The posting of the Theses was established in the historiography of the Reformation as the beginning of the movement by Philip Melanchthon in his 1548 Historia de vita et actis Lutheri.

During the 1617 Reformation Jubilee, the centenary of 31 October was celebrated by a procession to the Wittenberg Church where Luther was believed to have posted the Theses.

An engraving was made showing Luther writing the Theses on the door of the church with a gigantic quill.

[71] In 1668, 31 October was made Reformation Day, an annual holiday in Electoral Saxony, which spread to other Lutheran lands.