Robert Knight in an ironically entitled article, militant Secularism Distorts America's Heritage, distorts America's Heritage by offering David Barton's oft. cited phony quotes, attributed to, but never uttered by, our Founding Fathers. In all fairness to Barton, the primary source for many of these quotes is a book, America's God and Country: Encyclopedia of Quotations by William Federer, which Knight cites as his primary source. Here are the quotes Knight offers:
"The religion which has introduced civil liberty is the religion of Christ and His Apostles. ... This is genuine Christianity and to this we owe our free constitutions of government." - Noah Webster
"The reason that Christianity is the best friend of Government is because Christianity is the only religion that changes the heart." - Thomas Jefferson
"The highest story of the American Revolution is this: It connected in one indissoluble bond the principles of civil government with the principles of Christianity." - John Adams
"It cannot be emphasized too strongly or too often that this great nation was founded, not by religionists but by Christians, not on religions, but on the gospel of Jesus Christ." - Patrick Henry
Quotes 3 and 4 have been debunked as phony (see the above linked article, by Rob Boston) and I am almost certain that number 2 is phony as well (if not, someone please send the source for the original quotation). I am not sure about the Noah Webster quote, but given the tainted source, we have reason to doubt that one as well.
In any event, Jefferson referred to Knight's form of Calvinistic Christianity as "Daemonism." Jefferson despised this kind of Christianity and instead (wrongly) predicted that a much more liberal form of Christianity, Unitarianism, would sweep America and become dominant.
Knight also claims, "George Washington, [was] one of the most devout Christians ever to be President...." If that's true then we haven't yet had a devout Christian to take office because there is no evidence that Washington was "Christian" in anything other than a nominal sense. Washington was, what would then be referred to as a "deist," but now is better understood as a "theistic rationalist," which is a deist who believes in an interventionist God, but still rejects so many of the fundamental tenets of traditional Christianity -- the Divinity of Jesus, the inerrancy of revelation, the doctrine of eternal damnation, and others -- that it hardly qualifies as an "orthodox" version of the faith in any meaningful sense. Indeed, Washington refused to take communion in his Anglican Church (something orthodox Anglicans didn't do), leading his own ministers to conclude that he was a deist!
Knight also writes:
Schoolchildren need to be taught the truth: that America is free and allows the practice of all religions specifically because it was founded by Christians, who understood that man's powers over man should be limited because man is a sinful, fallen creature. Without that Biblical understanding, governments become despotic.
It was because of his Christian beliefs, not in spite of them, that Washington treasured and protected religious freedom.
I have seen this sentiment written over and over again by the theocrats that it prompted me to write an article, soon to be published in Liberty Magazine. In fact, the Calvinistic-Puritan, "Christian Nation" Protestants believed in the antithesis of religious freedom. Their civil law reflected the Biblical passages that prescribed punishment, up to and including the DEATH PENALTY (for instance, those who publicly worshipped false gods got that one), for publicly bucking religious orthodoxy.
The understanding of Christianity that demands religious freedom to which Knight refers was established by Roger Williams, himself an evangelical, who, luckily wasn't killed by the Puritans, but instead was banished to found Rhode Island for daring to question Massachusetts's notion of a "Christian Commonwealth." Williams also famously said, "No civil state or country can truly be called Christian, although the Christians be in it." In short, nations full of Christians concluded that religious freedom was necessary only when they rejected that civil governments are properly founded as "Christian" in a public sense.
[Update: Sandefur addresses the Jefferson quote. It's almost certain to be horseshit.]