“Rick Santorum is John Winthrop,” the historian and author John M. Barry was saying the other day.

Barry is in a unique position to make such a judgment. His most recent book, published last month, is entitled “Roger Williams and the Creation of the American Soul.” To call it a biography sells it short. What it is, really, is the history of an idea — an idea that Williams articulated before anyone else — about the critical importance of separating church from state. So revolutionary was this idea that it caused Williams to be banished from Massachusetts and to seek refuge in nearby Rhode Island, which he founded. In doing so, Williams created the first place in the Western world where people could believe in any God they wished — or no God at all — without fear of retribution.

In opposition to that idea, always, were Winthrop and the other Puritans who first came to Massachusetts. Puritans fled to America in the 1600s because they were being persecuted in England for their hard-edged, Calvinist beliefs, and their rejection of the Anglican Church. Having one’s ears cut off for having deviationist religious beliefs was one of the lesser punishments Puritans suffered; being locked up in the Tower of London, where death was a near certainty, was not uncommon.

Yet Winthrop and the other Puritans did not arrive on the shores of Massachusetts hungering for religious freedom. Rather, Winthrop’s “city on a hill” was meant to be, in Barry’s words, “an authoritative and theocentric state,” no less tolerant of any deviation of Puritan theology than England had been toward the Puritans. Even before Williams’s views about church and state were fully formed, he became an outcast in Massachusetts because he not only deviated from conventional Puritan theology but preached his beliefs from the pulpit — and then did not back down when confronted by the Massachusetts magistrates about his “errors.” Just as in England, the state served to enforce the dictates of the church.

Williams and Winthrop came to America about 150 years before the Constitution was signed. They are not the country’s founding fathers, but rather the founders’ forefathers. Although it unlikely that Thomas Jefferson, the strongest proponent for the separation of church and state among the founders, ever read the writings of Williams, he was, nonetheless, influenced by him, as his ideas had been carried forward by other thinkers over the next century.