James Madison was keenly aware of this when in his notes preparing for his famous Memorial & Remonstrance he wrote:
I probably reproduced more here than necessary for the thesis of this post. However, the different points of what's shown above encapsulate what is key to the controversy over how to understand the political theology of the American Founding. On point V6, John Adams endorses the "essential parts" only of the biblical canon position. Or perhaps that the canon in general is inspired, with particular words contained therein subject to dispute.
Adams was "up" on the state of late 18th Century biblical criticism in America and Europe. We know he rejected atheistic and deistic notions that attempted to debunk the concept of special revelation entirely just as he rejected "Athanasian" orthodox Trinitarian understandings of the canon.
Adams' third way was a path traveled by those who understood themselves to be Christian-Deists, unitarians, those in the "latitudinarian" wing of the Anglican Church. And they didn't necessarily speak in a univocal voice.
Still, this third way needed a solid ground on which to rest its case. That came in the form of belief in the existence of an overriding Providence, a future state of rewards and punishments, and something uniquely special about Jesus' place in history as embodying religious perfection.
As it relates to the canon of sacred scripture, certain parts were thus "essential" and not up for grabs. Other parts were either "suspected" or outright rejected. Unlike Thomas Jefferson, Bolingbroke and others, Adams preferred more to "suspect" or question rather than outright reject, for instance, the teachings of St. Paul and other parts of the Bible that didn't constitute the "essential parts."
On the other hand, Jesus' words were essential.
In his Marginalia, Notes on Memoirs of the Life and Writings of Arthur Ashley Sykes, D.D., Adams uses the term "pure" for what he views as those "essential," non-negotiable truths of the faith.
Against whom is this woe pronounced? How shall we know what is pure and uncorrupted but by by the first revelation? Is Sykes pure? Is Priestley pure? Is Lindsey pure? Is Paul pure? Is Jude pure? Is Locke pure? Is the great knight pure? Love God and Man! That is pure. Do as you would be done by! That is pure. Three units, are three times one! That is pure. All this can be understood by man, woman, and  children, rich and poor, without the study of three score years in a million volumes of philosophers, divines, and historians in Hebrew, Greek, Latin, Sanskrit, English, French, German, Spanish, Italian, and Russian.Did you see that? A.A. Sykes, Joseph Priestley, Theophilus Lindsey, St. Paul, the book of Jude, John Locke get lumped in the same box of questionable "purity." There may have been wisdom and truth in general in all of these sources, but still fallibility.
The essential, non-negotiable truths of Adams' creed are "Love God and Man! That is pure. Do as you would be done by!" In other words, the Sermon on the Mount.
Interestingly, Adams places rejection of the Trinity in the same box as he does the other "pure" teachings like the Sermon on the Mount. It's not just some hard to understand mystery over which good Christian might disagree. Those who affirm the Trinity indulge in a "supposition [that] is destructive of the foundation of all human knowledge and of all distinction between Truth and Falsehood."