By RAYMOND ZHONG

The Calvinist pilgrims who founded the New England colonies had rebelled against England by leaving it, but they were certainly not rebels against a firm social order or against the idea of authority itself. In England, laws against adultery were not enforced; in New England, adulterers might be executed, or whipped and forced to wear scarlet letters. The town of Hartford required its residents to rise from bed at the same hour in the morning. Massachusetts spurned "heathenish" practices to such a degree that it stopped using names for the days of the week, referring to them only by numbers.

Roger Williams, an early resident of Massachusetts who would go on to found the colony of Rhode Island, was uneasy about forced conformity to the Puritan mold, though not because he didn't like the mold. Williams agreed with the Massachusetts governors on most points of theology. He objected to the way in which the colonial government legislated what he felt was properly God's to dictate. Forced worship "stinks in God's nostrils," he wrote.

Williams felt that a society based on free religious exercise, uncompelled by earthly law, was truer to the vision of society in Scripture. As he clashed with the magistrates of Massachusetts, it became clear to him that, for such a society to exist, he would have to create it.

John Barry's "Roger Williams and the Creation of the American Soul" establishes Williams as a brave thinker and also a deft political actor—not a rare type in early American history but one we usually associate with the American Revolution, not the Puritan colonies.

Roger Williams was born in London around 1603. His suspicion of the excesses of political power was formed early on. He apprenticed with Sir Edward Coke, the jurist who told King James I that a monarch could make laws only through Parliament, not by royal prerogative. Williams left England for the New World in 1631, equipped with a Cambridge degree and, Mr. Barry writes, "the charm of great promise."

Williams was banished from Boston almost immediately. Gov. John Winthrop had offered him the position of assistant minister, but Williams turned it down, believing the Massachusetts church to be corrupt and insufficiently pious. Cast out, Williams spent time with New England's Indian tribes, learning their languages and befriending their chiefs. He took the peace he made with the Narragansetts and the Wampanoags as a sign that God had shown "merciful providence" to him in his distress.

By the time Williams co-founded Providence Plantation, in 1636, it had become clear to him that any sort of manmade stricture on worship was untenable, amounting to an unreasonable infringement on man's God-given conscience. The argument for religious toleration was not new, but it had mostly been made by persecuted sects, for the sake of self-preservation. Williams transformed toleration into a matter of principle.

Providence Plantation came into existence at a difficult period in New England history, when the colonists were waging a war against the Pequot tribe and England itself was lurching toward civil war. Still, Williams's convictions endured. When at last, in 1644, he secured a land patent to unite the separate colonies of Narragansett Bay, Rhode Island had been firmly established as a haven for religious outcasts, for those "troubled by conscience."

This vision of the New Jerusalem was at odds with the one on which previous English colonies had been founded. Winthrop had imagined America as a "city upon a hill," where men could flourish in God's image. But Winthrop's idea of liberty was "liberty to that only which is good," requiring individuals to "quietly and cheerfully submit, unto that Authority which is set over you." The "natural liberty" that Williams advocated was, to Winthrop's mind, a recipe for anarchy.

But Williams did not desire total permissiveness in his experimental society. Using words that Thomas Jefferson would echo more than a century later, Williams argued merely for a "hedge or wall of Separation between the Garden of the Church and the Wilderness of the world." Williams saw God's garden as too precious to be contaminated by the profanity of human politics. Williams's "wall of Separation" was meant to protect the church from the state, not the other way around. Even so, Mr. Barry puts Williams squarely among our great political thinkers, crediting him with bringing liberal democracy to the American colonies.

Why, then, does Williams languish in history's margins? The Rhode Island attitude toward religion did not catch fire right away, Mr. Barry notes. When Williams died in 1683, he was mourned in Rhode Island but not in the rest of New England. Jefferson and Madison got their liberalism mostly through Locke and the Enlightenment, though historians consider Williams to have influenced Locke's work to some degree.

There is another reason why Williams's place in the public imagination is small. Despite his forward-thinking ideas, his conception of the state was still by no means a modern, secular one. He assumed that public life required a religious core. For better or worse, neither Williams nor Winthrop would recognize his vision of a New Jerusalem in the United States today.

—Mr. Zhong is an editorial-page writer for The Wall Street Journal Europe.