The Preamble states,
We, therefore, the people of Massachusetts, acknowledging, with grateful hearts, the goodness of the great Legislator of the universe, in affording us, in the course of His providence, an opportunity, deliberately and peaceably, without fraud, violence or surprise, of entering into an original, explicit, and solemn compact with each other; and of forming a new constitution of civil government, for ourselves and posterity; and devoutly imploring His direction in so interesting a design, do agree upon, ordain and establish the following Declaration of Rights, and Frame of Government, as the Constitution of the Commonwealth of Massachusetts.
It is the right as well as the duty of all men in society, publicly, and at stated seasons to worship the Supreme Being, the great Creator and Preserver of the universe. ...
As the happiness of a people, and the good order and preservation of civil government, essentially depend upon piety, religion and morality ... the legislature shall ... require ... the institution of the public worship of God, and for the support and maintenance of public Protestant teachers of piety, religion and morality. ... And the people of this commonwealth have also a right to, and do, invest their legislature with authority to enjoin upon all the subjects an attendance upon the instructions of the public teachers aforesaid ... Any every denomination of Christians, demeaning themselves peaceably, and as good subjects of the commonwealth, shall be equally under the protection of the law: and no subordination of any one sect or denomination to another shall ever be established by law.
Article II of chapter II states, "no person shall be eligible to this office" of Governor "unless he shall declare himself to be of the Christian religion." Article I of chapter VI prescribes the oath for public oath, in which the candidate must swear that
I, A. B., do declare, that I believe the Christian religion, and have a firm persuasion of its truth...
Article I of section I of chapter V says
... Harvard College, in which university many persons of great eminence have, that by the blessing of God, been initiated in those arts and sciences, which qualified them for public employments, both in church and state: and whereas the encouragement of arts and sciences, and all good literature, tends to the honor of God, the advantage of the Christian religion, and the great benefit of this and the other United States of America ...
Now, there are several amendments to that constitution which have since removed all references to Christianity or Protestantism, and have removed all coercive elements. Article XI of the Amendments (1833) changed Article III to instead permit all freely-contracted religious associations, rather than mandating them as Article III did.
I also don't know the case law history of enforcement of this Constitution, whether before or after the Amendments changed it. How were Jews treated, for example? Article III conditioned the requirement to attend services on "provided there be any on whose instructions he attends"; would a Jew be exempted from Christian Church based on this? I don't know.
Furthermore, how was "Supreme Being, the great Creator and Preserver of the universe" interpreted in the case law? Was the Jewish G-d included in this, or was only the Christian G-d intended? I don't know.
But all these questions aside, it is very clear that Massachusetts was extremely religious, one way or the other. Realize that until Article XI of the Amendments was ratified in 1833, the Constitution of Massachusetts explicitly mandated that Protestant churches and Christian denominations be established and that attendance by the masses be enforced and compulsory.
Cf. the Maryland Toleration Act:
The Maryland Toleration Act, also known as the Act Concerning Religion, was a law mandating religious tolerance for trinitarian Christians. Passed on September 21, 1649 by the assembly of the Maryland colony, it was the first law requiring religious tolerance in the British North American colonies and created the first legal limitations on hate speech in the world. Historians argue that it helped inspire later legal protections for freedom of religion in the United States. ... As the first law on religious tolerance in the British North America, it influenced related laws in other colonies and portions of it were echoed in the writing of the First Amendment to the United States Constitution, which enshrined religious freedom in American law. ... The Act allowed freedom of worship for all trinitarian Christians in Maryland, but sentenced to death anyone who denied the divinity of Jesus.Now, the Maryland Toleration Act was repealed in 1654, reinstated briefly, and repealed permanently in 1692. My point is not that the Maryland Toleration Act was law in any given place (by contrast, the Constitution of the state of Massachusetts certainly was law!!). I'm just trying to indicate the general philosophical roots of America.
This is all objective historical fact.