Five centuries ago, Christians in Europe who hoped to go to heaven knew they might first have to spend a few thousand years in a fiery purgatory, where they would be purified of their outstanding sins.

It was not a pleasant thought, but the Catholic Church offered some hope: A cash offering to the local priest could buy an "indulgence" certificate, entitling the believer to a shorter purgatory sentence.

In practice, the money often went into the pockets of corrupt church officials and their political allies. So in 1517 a German monk named Martin Luther decided to protest the practice. On or about Oct. 31 of that year, he publicly presented 95 handwritten "theses" against the sale of indulgences.

Luther expected only to prompt a debate within Christian circles, but with that act he sparked a revolution. The Protestant Reformation that followed his protest upended the political and ecclesiastical order across Europe.

For the upcoming 500th anniversary of the Reformation, the Minneapolis Institute of Art (MIA) has mounted an exhibition that chronicles Luther's life and work. One of the objects on display is an actual 16th century indulgence chest, complete with iron plates, heavy hinges and five separate locks. People wishing to purchase an indulgence dropped their coins in a slot on the top of the box.

"It was meant to be shut tight," says Tom Rassieur, who curated the MIA exhibition.

More than 400 artworks and historical objects are on display in the exhibition, including some of Luther's personal possessions and archaeological artifacts from his personal residence in Eisleben, Germany. Many of the items have not been displayed outside Germany before, and the exhibition as a whole is the most comprehensive collection of Luther-related objects ever assembled in one place.

"When we were contacted by museum officials in Germany," says MIA director Kaywin Feldman, "our number one question was, 'How can we make this the best Luther show ever?' "

The exhibit makes clear that Luther's spectacular success was in large part a propaganda phenomenon. His broadside against Catholic Church practices might have gone unnoticed were it not for the introduction a few decades earlier of a new technology: the printing press. Luther's challenge to church authority was incendiary, and German printers immediately recognized a hot property.

"As an entrepreneurial venture, they set the 95 Theses into type, printed them and reproduced them," says Rassieur. "When they saw how rapidly they were selling, they made copies and copies and copies. It went viral."

The MIA exhibit includes several versions of the printed theses, including a pocket-sized edition just four pages long. One copy was printed in Basel, in present-day Switzerland, not more than two months after Luther posted his own handwritten version.

"That means Luther's words had already reached out hundreds of miles," Rassieur says. "When Luther's ideas started to spread, there was no way they could be stopped." No one knows how many copies of the 95 Theses were printed, but Rassieur says there were probably "thousands and thousands," given the number of editions that were immediately produced.

As with the Internet centuries later, Luther showed how a new information technology could change the world.

From Rome, orders were put out for Luther to be put on trial, presumably to be burned at the stake for heresy. He went into hiding. But he was never apprehended, and ultimately he became the most famous preacher of his day.

Among the items in the MIA exhibition is the actual pulpit from which Luther gave his last sermon. The structure is more than 20 feet tall, with a sounding board overhanging the rostrum like a roof. The pulpit had never before left the church in Eisleben where it was located, and moving and installing it in the Minneapolis museum was the most daunting challenge the curators faced.

As with the printed versions of the 95 Theses, the pulpit has major symbolic significance. It was Martin Luther who introduced the idea of a sermon or homily as a central part of the Christian worship service.

"Previously, you'd go to church, and the emphasis was on the Eucharist," Rassieur says, "the blessing of the bread and the wine. The priest would mostly be at the altar, with his back to the congregation, murmuring words in Latin, a language the worshippers would not understand.

"Luther changed things. He had the priest get up in a box and stand in a very visible place, addressing the congregation and speaking to them in plain language, in their native tongue. His whole philosophy was that you had to return to the word of God."

As someone who challenged authority and introduced a people's Christianity, Luther was a transformative figure in modern European history. He was also highly divisive, however, and he was personally responsible through his teachings and writings for the promotion of anti-Semitism. After originally reminding his followers that Jesus and his apostles were themselves Jewish and advocating outreach to the Jewish community, Luther concluded the effort was not likely to result in widespread Jewish conversions.

"At the end of his life, he went bonkers," says James Reston Jr., author of Luther's Fortress: Martin Luther and His Reformation Under Siege. "He wrote increasingly anti-Semitic tracts which later got used by the Nazis."

The dark phases of Luther's life are well documented in the MIA exhibition. The curators were assisted by an interfaith advisory committee, and some of Luther's most hateful writings are prominently displayed in the exhibition, including a copy of his infamous tract, On the Jews and Their Lies.

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