In doing research on the Founders & Religion, I'm struck how they raised many of the same moral problems with the God of fundamentalist Christianity that we freethinkers and secularists raise today.
This may surprise some readers; I consider myself to be pretty open minded on religious matters regarding whether there is any Truth to be found there, certainly more so than some of the militant atheists/materialists who I am sure read my blog. I am not an atheist and think it's entirely possible, likely even, that a supernatural force created the universe. But there are certain things to which I have closed my mind. For instance, I have closed my mind to the possibility that Allah called those 19 high-jackers to ram our airplanes into our buildings and rewarded them with 70 virgins in Heaven. Likewise I've closed my mind to the possibility that God would send the overwhelming majority of the human race to Hell for all of eternity, for not figuring out the "right" religion, for belonging to the "wrong" Church, not accepting Jesus as Savior and becoming "born-again," etc. And I have closed my mind to that possibility for the same reason that I have closed my mind to the first: Both would seem to indicate a malevolent, unjust God being in charge of the universe. And that cannot possibly be so.
And Jefferson and Adams thought the exact same thing. They believed in a kinder, more benevolent God than the God of fundamentalist Christianity. These Founders had utter contempt for John Calvin and Calvinism. And a big source their dispute with Calvin was his teachings on the doctrine of eternal damnation.
Here is a passage from an 1823 letter from Jefferson to Adams.
I can never join Calvin in addressing his god. He was indeed an Atheist, which I can never be; or rather his religion was Daemonism. If ever man worshipped a false god, he did. The being described in his 5. points is not the God whom you and I acknowledge and adore, the Creator and benevolent governor of the world; but a daemon of malignant spirit. It would be more pardonable to believe in no god at all, than to blaspheme him by the atrocious attributes of Calvin.
That little passage says many things. While Jefferson's God was a "benevolent governor of the world," Calvin's was a "daemon of malignant spirit." Something else... I've noted on this blog that whereas our Founders weren't orthodox in their religious beliefs, they did believe a religious citizenry to be superior to an irreligious one. While that's true, we should caution before we conclude that they therefore supported fanatical fundamentalist Christianity as being good for society. Jefferson's letter indicates that "it would be more pardonable to believe in no god at all, than to blaspheme him by the atrocious attributes of Calvin."
As Mark Lilla wrote in the NY Times, the Founders wanted the citizenry to be religious, but they also wanted religion to "liberalize  doctrinally, [and] become less credulous and dogmatic, more sober and rational."
It's also interesting to note that Jefferson claims that Adams believed in the same "benevolent God" that he does. I've read much of their correspondence, and I found this to be a pleasant surprise about Adams. Many are under the misconception that Adams was an orthodox Christian; he wasn't. His personally held religious views were almost identical to Jefferson's.
Here is Adams, again in correspondence with Jefferson, on his disbelief in the doctrine of eternal damnation and his distaste for Calvinism.
God has infinite wisdom, goodness, and power; he created the universe; his duration is eternal ... his presence is as extensive as space. It is said that he created this speck of dirt—the earth—and the human species for his glory. And then, the orthodox theologians say, he chose to make nine-tenths of our species miserable forever, for his greater glory.
Now, my friend Jefferson, can prophecies and miracles convince you or me that infinite benevolence, wisdom, and power created and preserves for a time, innumerable millions, only in the end to make them miserable forever, and for no other purpose than his own glory?
Wretch! What is glory? Is he ambitious? Does he want promotion? Is he vain, tickled with adulation, exulting and triumphing in his power and the sweetness of his vengeance? Pardon me, my Maker, for these awful questions…but I believe no such thing. My adoration for the author of the universe is too profound, too sincere. The love of God and his creation—delight, joy, triumph, exultation in my own existence—are my religion.
The Calvinist, the Athanasian [Rowe: formulators of the doctrine of the Trinity] divines ... will say I am no Christian. I say they are no Christians, and there the account is balanced.
Something else that has surprised me in my research is that not only did Adams and Jefferson possess nearly identical religious beliefs, Washington's, Franklin's, and Madison's religious beliefs differed little if in any way at all from Jefferson's and Adam's.