Chauncy claimed he could use Sola Scriptura to prove the falsity of the doctrines of original sin, the trinity and eternal damnation. That puts him in the "heretic," arguably "not Christian" box, from the perspective of the "orthodox." Gregg Frazer's PhD thesis has a lengthy write up on Chauncy that concludes his theology was "not Christian."
Chauncy's method was interesting. He embraced "reason" along with "revelation." Indeed he criticized the "Great Awakeners" for not being "reasonable" enough when he noted:
But in nothing does the enthusiasm of these persons discover itself more, than in the disregard they express to the dictates of reason.
He claimed he could show from the Bible alone that it did not teach the aforementioned orthodox doctrines. Chauncy would admit, though, that it was his own "reasoned interpretation" of the Bible that rejected these doctrines.
And this nuance sheds light on a dispute about Gregg Frazer's thesis occurring in the commentary at American Creation. Gregg's thesis argued the key Founders and patriotic preachers believed that, though reason and revelation generally agreed with one another and that some, much, but not all of the Bible was legitimately revealed, when the two appeared to conflict they resolved the conflict in favor of reason, not revelation. Hence reason trumped revelation. You certainly get this from Jefferson, J. Adams, and Franklin. But, as my friend Tom Van Dyke argues, those three said these things privately and regarding the others, especially in their public addresses, you don't see them claiming the Bible is fallible, that reason trumps its errors, etc.
Van Dyke is right in the sense that publicly the key FFs and the patriotic preachers like Chauncy, Jonathan Mayhew, Samuel West and many others, didn't go around calling the Bible errant and saying that human reason trumps it. It might not be what they SAID; but it's arguably what they DID. And like the key Founders, it's perhaps/probably what the patriotic preachers PRIVATELY thought.
On the surface they appeared to preach that reason and revelation agreed, that we must have a "reasoned" interpretation of the Bible because they same God who authored the Bible also authored NATURE (what man discovered from reason alone). But when the two appeared to conflict, they followed nature and made the Bible "fit" with the findings of man's reason.
I think one could argue that this is exactly how Chauncy, Mayhew and West all handled the Trinity, Eternal Damnation and Romans 13. Man's REASON, discovering NATURE, found (among other things) that 1) God is unitary, not Triune, 2) a benevolent God would not damn anyone to Hell for eternity, and 3) men have a right to rebel against tyrants. With that already settled, they went back and made their scriptural case for all three positions.
You can read Chauncy doing this in his classic The Mystery Hid From Ages and Generations which was his purported biblical case against eternal damnation. Perhaps in a later post we will read from its quotations and discuss whether it really is the Bible that teaches against eternal damnation or "reason" superseding certain parts of the Bible to get to that result.