"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."
Then go back and read the rest of the sections here. It's broken down nicely. Print it. READ IT. KNOW IT. We could all use a refresher, I'm certain.
This whole "separation of church & state" fiasco has been seized by the Left as a way to abolish Christianity entirely. They believe Christians have too much "power" in the U.S. (ironically, they don't understand that Christians don't believe true power comes from the government), and the ideals and morals that we try to advance interfere with their way of life. For example, they want to keep abortion legal, legalize gay marriage, fund embryonic stem cell research, etc. All of which are at odds with Christian moral principle.
We need to remember that the phrase "separation of church and state" is NOT in the Constitution at all. It came from a letter written by one man - Thomas Jefferson - in a letter to the Danbury Baptist Association, addressing some of their concerns over religious freedom. In fact, the purpose of his letter was to assure the Baptists that their religious freedoms would not be impeded by the government...not that they weren't allowed to practice religion because of the government! Which is ironic because the Left always uses that quote to try to inhibit prayer and religion, not the other way around.
You can see the full text of Jefferson's letter to the Danbury Baptists here. As you can easily see, it exhibits a "separation of church and state" as a means to afford individuals a right to freely express their religion. It is an assurance of freedom...not a threat that prayer is a violation of it.
Until the government begins imposing Christianity, Buddhism, Islam, Obamism, or any other "religion" upon us (think 1984), and forbids the practice of any other "non-sanctioned" religion, I believe the Founding Fathers would deem the National Day of Prayer worthy of our time and attention.