Over the weekend I bought Michael and Jana Novak's Washington's God and have thumbed through a little of it. (I also bought Yes - Songs from Tsongas - 35th Anniversary Concert). Though I've studied, in detail, Washington's religious beliefs, I'm sure the book will inform me of things about which previously I had not known.
But let me make a prediction: Whatever the conclusions the Novak's draw, the book will not demonstrate that Washington was an orthodox Trinitarian Christian; rather the facts will support Gregg Frazer's thesis that Washington was a Theistic Rationalist and his religious beliefs were more or less the same as Jefferson's, Franklin's, Adams's, and Madison's.
The book aptly demonstrates that Washington believed in a warm intervening Providence (hence he wasn't a strict Deist). But that is a tenet of theistic rationalism. The theistic rationalists were also theological Unitarians. And indeed, we get no evidence that Washington believed in the Trinity. In fact, Washington never referred to God in Trinitarian terms, and virtually never mentioned the words "Jesus Christ."
The only record of Washington mentioning the words "Jesus Christ" was in a Speech to the Delaware Chiefs given in 1779 where he stated
Brothers: I am glad you have brought three of the Children of your principal Chiefs to be educated with us. I am sure Congress will open the Arms of love to them, and will look upon them as their own Children, and will have them educated accordingly. This is a great mark of your confidence and of your desire to preserve the friendship between the Two Nations to the end of time, and to become One people with your Brethen of the United States. My ears hear with pleasure the other matters you mention. Congress will be glad to hear them too. You do well to wish to learn our arts and ways of life, and above all, the religion of Jesus Christ. These will make you a greater and happier people than you are. Congress will do every thing they can to assist you in this wise intention; and to tie the knot of friendship and union so fast, that nothing shall ever be able to loose it.
This seems to be pretty reasonable practical advice given to Indians for assimilating into the culture where the Christian religion was dominant.
Finally, on Novak's website he has a long quote from the eminent historian Gordon Wood, who, more or less, reads the facts the Novak's uncover in the same way that I do: Washington believed in a warm Providence, so he wasn't a "strict" Deist, but wasn't an orthodox Trinitarian Christian either. Wood writes:
I don't think in Washington's case that he held back anything. I think he just naturally lacked, what I would call, a religious sensibility, except that he did believe in God and, as Michael says, in Providence and the interposition of this God, but he was not what we call an evangelical Christian. He certainly rarely ever used the name of Jesus in any of his writings. So it's hard to see him as an evangelical or even a deeply religious person in the usual Christian sense. But nonetheless, he is religious; there is no secular mind there."