The Reformation was politically motivated rather than coming from religious and spiritual reasons

This week, people across the world are celebrating Halloween. But Tuesday, many people of faith marked another, far less spooky, celebration. October 31 was the 500-year anniversary of the day Martin Luther allegedly nailed his 95 theses — objections to various practices of the Catholic Church — to the door of a German church. This event is widely considered the beginning of the Protestant Reformation.

The event was celebrated across Germany, including in Luther’s native Wittenberg (T-shirts for sale there proudly proclaim, “Protestant since 1517!”), as well as by Protestants of all denominations worldwide. As the inciting incident for the entire Reformation, Luther’s actions came to define the subsequent five centuries of Christian history in Western Europe and, later, America: a story of constant intra-Christian challenge, debate, and conflict that has transformed Christianity into the diffuse, fragmented, and diverse entity it is today.

This week, Twitter has been full of users discussing Reformation Day. Some have used the opportunity to post jokes or funny memes about their chosen Christian denomination. Others are debating Luther’s legacy, including discussing the degree to which he either created modern Christianity as we know it or heralded centuries of division within Christian communities.

While Reformation Day is celebrated annually among some Protestants, especially in Germany, the nature of this anniversary has brought debate over Luther and the Protestant Reformation more generally into the public sphere.

So what exactly happened in 1517, and why does it matter?

What started as an objection to particular corruptions morphed into a global revolution

While the Catholic Church was not the only church on the European religious landscape (the Eastern Orthodox Churches still dominated in Eastern Europe and parts of Asia), by the 16th century, it was certainly the most dominant. The church had a great deal of political as well as spiritual power; it had close alliances, for example, with many royal houses, as well as the emperor of the Holy Roman Empire, which at that time encompassed much of Central Europe, including present-day Germany.

The church’s great power brought with it a fair degree of corruption. Among the most notable and controversial practices of that time was the selling of “indulgences.” For Catholics of that time, sin could be divided into two broad categories. “Mortal sin” was enough to send you to hell after death, while “venal sin” got you some years of purifying punishment in purgatory, an interim state between life on earth and the heavenly hereafter.

By the 16th century, the idea that you could purchase an indulgence to reduce your purgatorial debt had become increasingly widespread. Religious leaders who wanted to fund projects would send out “professional pardoners,” or quaestores, to collect funds from the general public. Often, the sale of indulgences exceeded the official parameters of church doctrine; unscrupulous quaestores might promise eternal salvation (rather than just a remission of time in purgatory) in exchange for funds, or threaten damnation to those who refused. Indulgences could be sold on behalf of departed friends or loved ones, and many indulgence salesmen used that pressure to great effect.

Enter Martin Luther. A Catholic monk in Wittenberg, Luther found himself disillusioned by the practices of the church he loved. For Luther, indulgences — and the church’s approach to sin and penance more generally — seemed to go against what he saw as the most important part of his Christian faith. If God really did send his only son, Jesus, to die on the cross for the sins of mankind, then why were indulgences even necessary? If the salvation of mankind had come through Jesus’s sacrifice, then surely faith in Jesus alone should be enough for salvation.

In autumn 1517 (whether the actual date of October 31 is accurate is debatable), Luther nailed his 95 theses — most of the 95 points in the document, which was framed in the then-common style of academic debate, objections to the practice of indulgences — to a Wittenberg church door.

His intent was to spark a debate within his church over a reformation of Catholicism. Instead, Luther and those who followed him found themselves at the forefront of a new religious movement known as Lutheranism. By 1520, Luther had been excommunicated by the Catholic Church. Soon after, he found himself at the Diet (council) of the city of Worms, on trial for heresy under the authority of the (very Catholic) Holy Roman Emperor Charles V. At that council, the emperor declared Luther to be an outlaw and demanded his arrest.

Political, economic, and technological factors contributed to the spread of Luther’s ideas

So why wasn’t Luther arrested and executed, as plenty of other would-be reformers and “heretics” had been? The answer has as much to do with politics as with religion. In the region now known as Germany, the holy Roman emperor had authority over many regional princes, not all of whom were too happy about submitting to their emperor’s authority.

One such prince, Frederick III, Elector of Saxony, “kidnapped” Luther after his trial to keep him safe from his would-be arrestors. In the years following the trial, and the spread of Luther’s dissent as the basis for a Lutheranism, Protestantism often became a means by which individual princes would signal their opposition to imperial power. And when a prince converted, his entire principality was seen to have converted too. This led, for example, to the catastrophic Thirty Years’ War from 1618 to 1648, in which conflict between pro-Catholic and pro-Lutheran German princes morphed into a pan-European war that killed up to 20 percent of Europe’s population.

As it happens, the term “Protestant” began as a political rather than theological category. It originally referred to a number of German princes who formally protested an imperial ban on Martin Luther, before becoming a more general term for reformers who founded movements outside the Catholic Church.

Meanwhile, Luther was able to spread his ideas more quickly than ever before due to one vital new piece of technology: the printing press. For the first time in human history, vast amounts of information could be transmitted and shared easily with a great number of people. Luther’s anti-clerical pamphlets and essays — which were written in German, the language of the people, rather than the more obscure and “formal” academic language of Latin — could be swiftly and easily disseminated to convince others of his cause. (The relationship between Luther and the printing press was actually a symbiotic one: The more popular Luther became, the more print shops spread up across Europe to meet demand.)

Luther’s newfound popularity and “celebrity” status, in turn, made him a much more difficult force for his Catholic opponents to contend with. While earlier would-be reformers, such as John Hus, had been burned at the stake for heresy, getting rid of someone as widely known as Luther was far more politically risky.

Luther’s success, and the success of those who followed him, is a vital reminder of the ways politics, propaganda, and religion intersect. Something that began as a relatively narrow and academic debate over the church selling indulgences significantly changed Western culture. Luther opened the floodgates for other reformers.

Although Luther can be said to have started the Reformation, he was one of many reformers whose legacy lives on in different Protestant traditions. Switzerland saw the rise of John Calvin (whose own Protestant denomination, Calvinism, bears his name). John Knox founded the Presbyterian Church of Scotland. Each denomination of Protestantism had its own specific theology and approach. But not all Protestant reformations were entirely idealistic in nature: King Henry VIII famously established the Church of England, still the state church in that country today, in order to annul his marriage to Catherine of Aragon and marry Anne Boleyn.

Nearly all Protestant groups, however, shared Luther’s original objections to the Catholic Church — theological ideals that still define the Protestant umbrella today.

The most important of these is the idea that salvation happens through faith alone. In other words, nothing — not indulgences, not confession or penance, not even good works — can alter the course of a person’s salvation. For Protestants, salvation happens through divine grace received through faith in Jesus Christ. The second of these is the idea that biblical Scripture, and a person’s individual relationship with the Bible, is the most important source of information about God and Christian life. (This is in stark contrast with the Catholic Church, in which a wider body of church teaching and church authority play a major role.)

While it would be too simplistic to say that Protestants as a whole favor individualism and autonomy over established tradition, it’s fair to say that most Protestant traditions place a greater premium on individuals’ personal religious experiences, on the act of “being saved” through prayer, and on individual readings of Scripture, than do Catholics or members of orthodox churches.

Other differences between Catholic and Protestant theology and practice involve the clergy and church. Protestants by and large see the “sacraments,” such as communion, as less important than their Catholic counterparts (the intensity of this varies by tradition, although only Catholics see the communion wafer as the literal body of Christ). Protestant priests, likewise, are not bound by priestly celibacy, and can marry.

That said, for many Christians today, differences are cultural, not theological. Earlier this fall, a study carried out by the Pew Research Center found that average Protestants more often than not assert traditionally Catholic teachings about, among other things, the nature of salvation or the role of church teaching.

Protestantism today still bears the stamp of Luther

Today, about 900 million people — 40 percent of Christians — identify as Protestant around the world. Of these, 72 million people — just 8 percent — are Lutherans. But Lutheranism has still come to define much of the Protestant ethos.

Over the centuries, more forms of Protestantism have taken shape. Several of them have had cataclysmic effects on world history. Puritanism, another reform movement within the Church of England, inspired its members to seek a new life in the New World and helped shape America as we know it today. Many of these movements classified themselves as “revivalist” movements, each one in turn trying to reawaken a church that critics saw as having become staid and complacent (just as Luther saw the Catholic Church).

Of these reform and revivalist movements, perhaps none is so visible today in America as the loose umbrella known as evangelical Christianity. Many of the historic Protestant churches — Lutheranism, Calvinism, Presbyterianism, the Church of England — are now classified as mainline Protestant churches, which tend to be more socially and politically liberal. Evangelical Christianity, though, arose out of similar revivalist tendencies within those churches, in various waves dating back to the 18th century.

Even more decentralized than their mainline counterparts, evangelical Christian groups tend to stress scriptural authority (including scriptural inerrancy) and the centrality of being “saved” to an even greater extent than, say, modern Lutheranism. Because of the fragmented and decentralized way many of these churches operate, anybody can conceivably set up a church or church community in any building. This, in turn, gives rise to the trend of “storefront churches,” something particularly popular in Pentecostal communities, and “house churches,” in which members meet for Bible study at one another’s homes.

The history of Christianity worldwide has, largely, followed the Luther cycle. As each church or church community becomes set in its ways, a group of idealistic reformers seeks to revitalize its spiritual life. They found new movements, only for reformers to splinter off from them in turn.

In America, where mainline Protestantism has been in decline for decades, various forms of evangelical Protestantism seemed to flourish for many years. Now evangelicals — particularly white evangelicals — are finding themselves in decline for a variety of reasons, including demographic change and increasingly socially liberal attitudes on the part of younger Christians. Meanwhile, social media — the printing press of our own age — is changing the way some Christians worship: Some Christians are more likely to worship and study the Bible online or attend virtual discussion groups, while in other churches, attendees are encouraged to “live-tweet” sermons to heighten engagement.

What happens next is anyone’s guess.

But if the history of Lutheranism is anything to go by, we may be due for another wave of reformation before too long.