Kenneth C. Davis: Why the U.S. is Not a Christian Nation

Kenneth C. Davis is the author of "Don't Know Much About History: Anniversary Edition" (HarperCollins). He posts regularly at his blog at http://www.dontknowmuch.com/.

(CNN) -- As America celebrates its birthday on July 4, the timeless words of Thomas Jefferson will surely be invoked to remind us of our founding ideals -- that "All men are created equal" and are "endowed by their Creator" with the right to "Life, Liberty and the pursuit of Happiness." These phrases, a cherished part of our history, have rightly been called "American Scripture."

But Jefferson penned another phrase, arguably his most famous after those from the Declaration of Independence. These far more contentious words -- "a wall of separation between church and state" -- lie at the heart of the ongoing debate between those who see America as a "Christian Nation" and those who see it as a secular republic, a debate that is hotter than a Washington Fourth of July.

It is true these words do not appear in any early national document. What may be Jefferson's second most-quoted phrase is found instead in a letter he sent to a Baptist association in Danbury, Connecticut.

While president in 1802, Jefferson wrote: "Believing with you that religion is a matter which lies solely between Man and his God, that he owes account to none other for his faith or his worship, that the legitimate powers of government reach actions only, and not opinions, I contemplate with sovereign reverence that act of the whole American people which declared that their legislature should 'make no law respecting an establishment of religion, or prohibiting the free exercise thereof,' thus building a wall of separation between Church and State ... "...