Reformation Day is a religious holiday celebrated on October 31 in remembrance of the Reformation, particularly by Lutheran and some Reformed church communities. It is a civic holiday in Slovenia (since the Reformation contributed to its cultural development profoundly, although Slovenes are mainly Roman Catholics) and in the German states of Brandenburg, Mecklenburg-Vorpommern, Saxony, Saxony-Anhalt, and Thuringia. It is also a national holiday in Chile since 2008.
In the United States churches often transfer the holiday, so that it falls on the Sunday (called Reformation Sunday) on or before October 31, with All Saints' Day moved to the Sunday on or after November 1.
On 31 October 1517, Martin Luther wrote to Albrecht, Archbishop of Mainz and Magdeburg, protesting against the sale of indulgences. He enclosed in his letter a copy of his "Disputation of Martin Luther on the Power and Efficacy of Indulgences," which came to be known as The 95 Theses. Hans Hillerbrand writes that Luther had no intention of confronting the church, but saw his disputation as a scholarly objection to church practices, and the tone of the writing is accordingly "searching, rather than doctrinaire." Hillerbrand writes that there is nevertheless an undercurrent of challenge in several of the theses, particularly in Thesis 86, which asks: "Why does the pope, whose wealth today is greater than the wealth of the richest Crassus, build the basilica of St. Peter with the money of poor believers rather than with his own money?"
Luther objected to a saying attributed to Johann Tetzel that "As soon as the coin in the coffer rings, the soul from purgatory [also attested as 'into heaven'] springs." He insisted that, since forgiveness was God's alone to grant, those who claimed that indulgences absolved buyers from all punishments and granted them salvation were in error. Christians, he said, must not slacken in following Christ on account of such false assurances.
According to Philipp Melanchthon, writing in 1546, Luther "wrote theses on indulgences and posted them on the church of All Saints on 31 October 1517", an event now seen as sparking the Protestant Reformation. Some scholars have questioned Melanchthon's account, since he did not move to Wittenberg until a year later and no contemporaneous evidence exists for Luther's posting of the theses. Others counter that such evidence is unnecessary because it was the custom at Wittenberg university to advertise a disputation by posting theses on the door of All Saints' Church, also known as "Castle Church".
The 95 Theses were quickly translated from Latin into German, printed, and widely copied, making the controversy one of the first in history to be aided by the printing press. Within two weeks, copies of the theses had spread throughout Germany; within two months throughout Europe.
Luther's writings circulated widely, reaching France, England, and Italy as early as 1519. Students thronged to Wittenberg to hear Luther speak. He published a short commentary on Galatians and his Work on the Psalms. This early part of Luther's career was one of his most creative and productive. Three of his best-known works were published in 1520: To the Christian Nobility of the German Nation, On the Babylonian Captivity of the Church, and On the Freedom of a Christian.
History of the observance of Reformation Day 
The parish order for the New Church in Regensburg states that the Reformation of the city is to be observed the first Sunday after October 15, every year. This document may be from 1567, however the dating is uncertain. The 1569 church order in Pomerania states that the Reformation was to be observed on St. Martin's Day, which falls on November 11. The hundredth anniversary of the Reformation, celebrated throughout the Protestant areas of Germany, was observed from October 31 to November 1, 1617, but a standard annual observance began much later, sometime after the two hundredth anniversary commemoration in 1717.
Lutheran church 
Within the Lutheran church, Reformation Day is considered a lesser festival, and is officially referred to as The Festival of the Reformation. Until the 20th century, most Lutheran churches celebrated Reformation Day on October 31, regardless of which day of the week it occurred. Today, most Lutheran churches transfer the festival, so that it falls on the Sunday (called Reformation Sunday) on or before October 31 and transfer All Saints' Day to the Sunday on or after November 1.
The liturgical color of the day is red, which represents the Holy Spirit and the Martyrs of the Christian Church. Luther's hymn, A Mighty Fortress is our God is traditionally sung on this day. It is also traditional in some Lutheran schools for schoolchildren to hold Reformation Day plays or pageants that re-enact scenes from the life of Martin Luther. The fact that Reformation Day coincides with Halloween may not be mere coincidence. Halloween, being the Eve of All Saints' Day might have been an entirely appropriate day for Luther to post his 95 Theses against indulgences since the castle church would be open on All Saints' Day specifically for people to view a large collection of relics. The viewing of these relics was said to promise a reduction in time in purgatory similar to that of the purchase of an indulgence.
Reformation Day (Reformationsfest) was celebrated in Leipzig in Bach's time with a service, for which he composed cantatas, including in 1725 Gott der Herr ist Sonn und Schild, BWV 79, and later Ein feste Burg ist unser Gott, BWV 80.
- "Johann Tetzel," Encyclopædia Britannica, 2007: "Tetzel's experiences as a preacher of indulgences, especially between 1503 and 1510, led to his appointment as general commissioner by Albrecht, archbishop of Mainz, who, deeply in debt to pay for a large accumulation of benefices, had to contribute a considerable sum toward the rebuilding of St. Peter's Basilica in Rome. Albrecht obtained permission from Pope Leo X to conduct the sale of a special plenary indulgence (i.e., remission of the temporal punishment of sin), half of the proceeds of which Albrecht was to claim to pay the fees of his benefices. In effect, Tetzel became a salesman whose product was to cause a scandal in Germany that evolved into the greatest crisis (the Reformation) in the history of the Western church."
- "BBC Religion & Ethics - In Pictures: Martin Luther, Wittenberg and the Reformation". Bbc.co.uk. 1 January 1970. Retrieved 31 October 2012.
- Hillerbrand, Hans J. "Martin Luther: Indulgences and salvation," Encyclopædia Britannica, 2007.
- Bainton, Roland. Here I Stand: a Life of Martin Luther. New York: Penguin, 1995, 60; Brecht, Martin. Martin Luther. tr. James L. Schaaf, Philadelphia: Fortress Press, 1985–93, 1:182; Kittelson, James. Luther The Reformer. Minneapolis: Augsburg Fortress Publishing House, 1986),104.
- Brecht, 1:200–201.
- Iserloh, Erwin. The Theses Were Not Posted. Toronto: Saunders of Toronto, Ltd., 1966; Derek Wilson, Out of the Storm: The Life and Legacy of Martin Luther, London: Hutchinson, 2007, ISBN 978-0-09-180001-7, 96.
- Junghans, Helmer. "Luther's Wittenberg," in McKim, Donald K. (ed.) The Cambridge Companion to Martin Luther. New York: Cambridge University Press, 2003, 26.
- Brecht, Martin. Martin Luther. tr. James L. Schaaf, Philadelphia: Fortress Press, 1985–93, 1:204–205.
- Spitz, Lewis W. The Renaissance and Reformation Movements, St. Louis: Concordia Publishing House, 1987, 338.
- Revelation 14:6