See this book, pp. 55-64.
Here is DANIEL EMERSON on the good Reverend:
During the Revolution, Mr. Cummings showed himself an earnest friend of his country's Independence. Fully convinced that the cause of the Colonies was a righteous cause, and that it was the duty of every man, whatever might be his profession or relations, to aid it to the extent of his ability, he laboured, both in the pulpit and out of it, to diffuse the patriotic spirit, and strengthen the hands of those on whom the direction cf the public concerns more immediately devolved. In 1783, the memorable year that witnessed the close of the War, he preached the Annual Sermon before the Legislature,—a sermon characterized by the most enlightened, patriotic views. The town of Billerica testified their high appreciation of his knowledge and good judgment in civil matters, by appointing him a delegate to the Convention which framed the Constitution of Massachusetts.
Here is THE REV. JOSEPH RICHARDSON on the man:
In his theological views he was an Arminian, and I suppose an Arian also; though he seldom dwelt much on points of controversy in the pulpit. I think he had no sympathy with any system that does not recognize the mediation ot Christ as the grand feature of the Christian economy. He exercised great kindliness of feeling towards those commonly called orthodox, and was on terms of exchange with a number of them till near the close of his active ministry.
And here is THE REV. ARIEL ABBOT, D. D. on him:
I cannot say much of him as a Preacher from actual knowledge, my opportunities for hearing him having bean very limited, but I am safe in saying that his pulpit performances were much above the average standard of his day. His manner was simple, earnest and effective. His sermons were generally practical but argumentative, nor did he hesitate at all, on what he deemed suitable occasions, to state clearly his views of Christian doctrine. Some of his published sermons bear marks of a mind, trained not only to vigorous but profound thought. In his religious opinions he was decidedly an Arminian, and, as I have always understood, an Arian. He regarded Calvinism, in all its forms, with no inconsiderable aversion. I remember to have heard him speak of Edwards' Treatise on the Will, as being, in his opinion, nothing better than fatalism; and he added, with his characteristic earnestness, that, if he were an Atheist, he should want no better arguments than that work supplied, to sustain his atheistical theory.
Finally FROM THE REV. NATHANIEL WHITMAN:
The theological controversy of Dr. Cummings' day related, I suppose, more especially to the subject of Moral Agency. In this controversy, he was prominent among those divines who maintained the Arminian view of the subject. He examined Edwards on the Will with great care, and wrote a Review of it, which he highly valued, containing condemnatory strictures. A few years after he was ordained, he became dissatisfied with the Trinitarian views in which he had been educated; and, having procured Waterland, and whatever other standard authors were within his reach, he spent a good part of a year in a critical examination of the subject. Not being satisfied with the result, he betook himself to the diligent study of the sacred records; and he finally rested in the conclusion that the revealed doctrine is that there is one God, the Father, and one Mediator, the Lord Jesus Christ. He bad no fondness for any human theory whatever on the subject of the union of the Father and Son; though he certainly was not a Humanitarian.