When the Puritans who were led by John Winthrop arrived in Massachusetts in 1630, they brought with them a royal charter. This charter, or patent, as they called it, entitled them to set up a provisional government for the Massachusetts Bay Colony and make whatever laws they needed so long as those laws were not contrary to the laws of England.
According to the charter, freemen were to meet and choose a governor and any other elected officials. "Freeman" was defined in the charter as any shareholder in the Massachusetts Bay Company, the group financing the colony. In May 1631, at the second meeting of the General Court set up by the colonists as a legislative and governing body, the freeman's oath was taken by 116 male colonists--just about all of the adult males of the small colony.
But at the same time that all these men were given the title and privileges of freemen, the officers of the Company decided amongst themselves that in the future, only church members would be allowed to become freemen. At that time, attending a Puritan church and being baptised in it did not make you a member. A member was someone who had completed a long and arduous spiritual journey toward Grace, and who had publicly narrated that experience and its end results before their church congregation, and had that statement accepted by the congregation.
As a result, there were relatively few members of Puritan churches. There were plenty of attendees, most of them utterly devoted to their church and their religion, but few people had the courage or the certainty to make the public statement required for membership.
So to restrict freemanship to church members drastically reduced the number of freemen in MBC. It also was a crossing of church and state lines that was very unusual in MBC. Why was it done?
Winthrop later said that he did it because he could see that "member of the Massachusetts Bay Company" was a definition that would soon include tens of thousands of men--every adult male resident of MBC. That was too many people to gather in one place to elect officers. Adult male residents who were also church members could be counted on to be respectable citizens, and also of an easily manageable number.
But this set-up was soon called into question by the colonists. At the very next meeting of the General Court, in May 1632, the original system of having freemen choose the assistants or magistrates who ran the Court, then having those assistants choose the governor, was replaced with a new system where the governor and assistants were chosen each year by the freemen assembled in General Court.
In May 1634, the people went further. Representatives to the General Court demanded to see the colony's charter. They felt pretty sure that the King had not set church membership as a requirement for freemanship. Now they were challenging Wintrhop and the magistrates.
Winthrop, who owned the only copy and kept it in his private papers at home, had deliberately kept the charter's terms secret from the people. The charter not only did not require church membership for freemen, it also allowed the freemen to make laws at the General Court, to act as a legislature. As Winthrop set it up, freemen of MBC sent their deputies to the GC only to present cases or appeals for action. The assistants and governor made all the laws.
Confronted by angry freemen, Winthrop made his argument that "when the patent was granted the number of freemen was supposed to be so few as they might well join in making laws, but now they were grown to so great a body as it was not possible for them to make or execute laws, but they must choose others for that purpose."
Winthrop was proposing just the system we have in the U.S. today, where we elect representatives to our Congress since we can't all go to Washington to make our own laws. While the freemen seemed to have accepted this, they still protested the requirement of church membership , and they also rejected the system approved by Winthrop, in which there were very few if any laws written down in a code of law. Winthrop much preferred to have each governor make decisions about how to keep the peace and enforce social justice on a case-by-case basis.
Over the years the men of the Massachusetts Bay Colony chipped away at the government Winthrop created. They eventually wrote a code of law, the Body of Liberties (1641), and kept hammering away at the church membership requirement of freemen. "They charge that the liberties and privileges in our charter belong to all freeborn Englishmen, inhabitants here, whereas they are granted only to such as the governor and company shall think fit to receive into that fellowship..." wrote Winthrop in 1646.
The church membership requirement would not be removed until 1664, when Charles II sent commissioners to MBC to oversee the colony. To avoid being taken over as a royal colony by Charles II, who would be removed from the throne for his Catholicism, the Puritans dropped the church membership requirement for freemen.
Why did Winthrop, who in all other ways promoted the separation of church and state, stick to this church membership requirement for freemanship? Why did it remain in place for years after his death?
One reason was that most Puritans in MBC agreed with the policy. They were, after all, people who had given up everything to live in a Puritan state. It was also a way to guard the colony's independence from England, where Parliament even during the Civil War was hostile toward the religion practiced in MBC. Having representatives who were certified New England Way Puritans assured the colony that its unique goals would continue to be met.
It is still a strange set-up, to require freemen at the legislative body to be church members, but refusing to let clergy join the GC, or to let the GC make church laws. It was a delicate balance that did not last long.