Alec Ryrie is the author of "Protestants: The Faith That Made the Modern World" and professor of Christian history at Durham University in England.

(CNN) If you're a Protestant, the anniversary of the revolution Martin Luther set in motion 500 years ago this Tuesday is a big deal. But even if you're not, it should be. The Reformation was one of the decisive events that made the world we live in, for better or worse.

Luther and his followers weren't trying to reshape the world: they were trying to save it. They had a gospel to proclaim and thought the end was near. But in their urgency they trampled down the walls that had kept life in Western Christendom neatly ordered.

Luther outflanked the power of the Catholic Church hierarchy with a new communications technology, the printing press, that allowed him to speak directly to the people. When he was finally dragged before the assembled majesty of church and empire in 1521 and ordered to renounce his errors, he refused, insisting that his conscience was captive to the Word of God, a higher authority than any pope, bishop or king.

Suddenly, everyone had a voice and no one could tell anyone else what to believe. Luther's radical appeal to the total supremacy of personal faith would trigger nearly 200 years of religious warfare.

If you're inclined to believe that our modern divisions go back to the way Luther smashed all order and authority: well, no one can tell you you're wrong. But if you think modern life is more than an endless bad-tempered argument, you may concede that Luther's Reformation gave us a few useful, if largely, unexpected gifts. Let me propose three:

1. Free inquiry

Luther wasn't an apostle of free speech. He wanted Christians to believe the truth, not whatever they wanted. But by insisting that all human authority was provisional and that conscience can be constrained only by the Bible and the Holy Spirit, he ensured that Protestants who try to police the boundaries of acceptable argument will in the end always fail.

Protestantism has given us not a paradise of free speech, but an open-ended, undisciplined argument. It has continuously generated new ideas, revived old ones and questioned its own orthodoxies.

To take the iconic example: slavery, which for centuries Christians had assumed was a necessary evil or simply a fact of life. A few Protestants in the 1700s and many more in the 1800s reached a new conviction: that slavery was an absolute and intolerable evil. The arguments and battles were bitter, but in the end the old orthodoxy was overthrown. Censorship was worn down by Protestants' refusal to shut up when told to, and by their bare-knuckle style of public argument.

Protestant universities and scholars also led the way in the emergence of the new natural sciences in the 16th and 17th centuries. And slowly, reluctantly, one notion a few radical Protestants put about -- that freedom of speech and of worship were actually good things, not just unavoidable necessities to be tolerated -- became a new orthodoxy.

2. Democracy

Luther would have choked on his beloved German beer had you told him that he would lead the world toward democracy. Like virtually everyone of his time, he found the idea horrifying.

But Luther wasn't the last Protestant to defy a hostile government. The movement he started led relentlessly in that direction. Protestants asserted not the right to choose their rulers, but the duty to challenge them. In performing that duty, the Scottish radical John Knox wrote in 1558, "all man is equal."

He didn't mean that the way we would understand it today, and he very definitely meant men and not women. But the idea had a life of its own. A generation after Knox, the Scottish King James VI was accusing his Protestant subjects of plotting a "Democratic form of government."

It wasn't true. They favored monarchy, good order and social stability. But their rulers had an intolerable tendency to defy God's will. Again and again, they were forced reluctantly to take matters into their own hands. They insisted that their voices be heard, and, when forced to, they took up arms against rulers who persecuted them. If we all stand equally before God, it is hard not to conclude that we should all have a voice before this world's rulers.

Left to itself, this notion could have led to the creation of self-righteous theocracies like the one some New England Puritans tried to build. But those have been rare, partly because Protestants are so ready to quarrel, but also because of the Reformation's third legacy to the modern world.

3. Limited government

Protestants have sometimes confronted or overthrown their rulers, but their most constant political demand is simply to be left alone.

Going back to Christianity's roots in ancient Rome, they have tried to carve out a spiritual space where political authority does not apply and have insisted that that space, the kingdom of God, matters far more than this world's sordid and ephemeral quarrels.

The results are paradoxical. Protestants have often been obedient subjects to thoroughly noxious rulers, taking no interest in politics so long as their own separate sphere is respected. They have also given unexpectedly stubborn opposition to rulers who won't respect their demand to be free of government intrusion. In the process, they helped give the modern world the counterintuitive notion of limited government: the principle that a government's first duty is to get out of the way of its people's lives as much as it can. It's a principle they wove into the DNA of the United States.

If Protestantism has given the modern world these three legacies, did it also give us a fourth one, capitalism?

The German sociologist Max Weber famously argued that the "Protestant work ethic" produced the modern economy, and though his evidence didn't really add up, the idea won't go away.

Capitalism first emerged in a group of Protestant countries: the Netherlands, Britain and the United States. In modern times, the years when South Korea's economy grew from $2.7 billion to $230 billion (1962-89) are the same years when the proportion of Protestants in the country grew from 2.5% to 27%. The Protestant surge in Latin America seems to be matched by a similar surge of private enterprise.

"Max Weber," the sociologist Peter Berger said, "is alive and well and living in Guatemala."

As Weber pointed out, capitalism is a system of "restless activity."So is Protestantism. Protestant activism isn't always economic, but Protestants do have a certain itchy instability, a restless, argumentative search for better, truer, purer.

Protestants are forever seeking out new sins or striving to recover old virtues. That self-perpetuating dynamo of dissatisfaction and yearning has certainly had economic effects, and has meant that Protestantism has thrived most during periods of rapid or wrenching social change.

It also means that its behavior is unpredictable. You can never tell where these restless consciences are going to go next. Politicians who imagine they have Protestants in their pockets should beware