Let's start with the painfully obvious. The First Amendment to the U.S. Constitution says:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof...It's a prohibition against the Federal .gov establishing a State-sponsored church. It's freedom of religion, not freedom from religion.
Then I was asked, aren't all the references to God in the Declaration and the Constitution in conflict with that statement?
Of course not (and I realize that, in many cases, I'm preaching to the choir). The Founders made it very clear that they recognized the hand* of God in the course of establishing the new Republic.
But but but ... what about John Adams' statement:
Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other.
That's even easier. Moral people, it says; not "Christians". Please notice that the Constitution forces no religion on any person. There is no clause that says "Believe as I do (or as the .gov does) or we'll kill or punish you."
A gentleman who probably heard about this from the cradle on up, said the following -
The highest glory of the American Revolution was this; it connected in one indissoluble bond the principles of civil government with the principles of Christianity.
From the day of the Declaration ... they (the American people) were bound by the laws of God, which they all, and by the laws of The Gospel, which they nearly all, acknowledge as the rules of their conduct.
~ John Quincy Adams
Principles and natural laws. A code of conduct. Not some particular religious belief.
They believed that if one conducted his/her affairs in accord with the code of Biblical behavior, that one would have no problem supporting the laws of the United States or its Constitution. (Of course, they also believed that the new federal government would make primarily just and moral laws, but that's another story.)
Not a theocracy, ladies and gentlemen, but a Constitutional Republic with citizens who conduct themselves civilly by means of moral precepts described in the Bible.
It's so simple, only a theologian** could screw it up.
*Or finger, as G. Washington put it. Take your pick.
**Or a historian. Just sayin'.