Such is my veneration for every religion that reveals the attributes of the Deity, or a future state of rewards and punishments, that I had rather see the opinions of Confucius or Mahomed inculcated upon our youth, than see them grow up wholly devoid of a system of religious principles. But the religion I mean to recommend in this place, is that of the New Testament.
Rush was an interesting character. He was an orthodox Trinitarian Christian and said certain things which sound "Christian Nation" like. Yet, his orthodox Christianity was liberal and enlightened for the era. He was a theological universalist, believing all men would be saved through Christ's universal (as opposed to limited) atonement. And he thought the New Testament abolished the death penalty.
Rush described his creed as "a compound of the orthodoxy and heterodoxy of most of our Christian churches."
One thing that interests me about Rush's first quotation is his idea that Confucianism "reveals the attributes of the Deity, or a future state of rewards and punishments...." That was the deistic or theistic minimum that many key and non-key Founders -- not just the heterodox rationalist unitarians, but some/many orthodox figures as well -- believed most if not all world religions adhered to.
This was the idea of "natural religion" -- that all good men of all religions believe in Providence and a future state of rewards and punishments. That man's "reason" discovered this. And, as it were, such Providentialism existed beyond the Abrahamic, traditionally thought of monotheistic religions.
The way natural religion "fit" with Christianity was the Jewish and Christian scriptures helped to further clarify what man could discover from reason alone.
I question whether it's sound theology to "find" monotheism outside of the Jewish, Muslim, and Christian traditions (broadly defined). But they did. John Adams "found" Providentialism in, among other places, Hinduism and Greek God worship. Hinduism perhaps could be thought of as monotheistic. I've heard some Hindus argue their thousands of gods are really manifestations of the one God of the universe. This seems like Trinitarian logic taken to its ultimate extreme (instead of three manifestations of one God, it's thousands).
Also, for obvious reasons [Western Civ. has Greco-Roman along with Judeo-Christian origins AND the FFs highly venerated such Greco-Roman noble paganism], the way the Founders' universal monotheism fit with classical Greece and Rome interests me.
It may be a stretch to say, as John Adams did, Zeus worship is a "Christian principle." However, what about the ancient philosophers like Aristotle and Socrates or the Stoics of Rome like Cinncinatus, Cicero and Seneca?
It is my (albeit limited) understanding that many of these wise Ancients did not worship the city gods like Zeus or his Roman moniker Jupiter. Isn't that what Socrates was executed for?
Yet, they weren't atheists either? They did believe in some kind of metaphysical Providence?
So men like Aristotle, Socrates, Cicero and Seneca perhaps could be said to have worshipped the God of the Jewish and Christian Scriptures without knowing more about Him.
That's one way to view it.
I rarely, however, hear the evangelical promoters of the "Christian Nation" thesis expounding theology like this. Roman Catholics, maybe.
Evangelicals are more likely to say Aristotle, Cicero, the Hindus and Confucians DIDN'T worship the God of the Bible, were/are in a state of spiritual darkness period.
The Founders would have disagreed.