We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.
The Constitution rules the day-to-day life of the United States, but the Declaration of Independence rules its spirit — setting forth a philosophy (not original, but originally expressed) that government served the people, not the other way around, and that all individuals had divinely-granted rights, not privileges subject to the whims of the rulership.
It is an underlying philosophy that may sometimes fade from view, but always remains in the American heart. It is a philosophy that politicians, pundits, demogogues, agitators, and extremists of all stripes must remember, at their peril. And it is a lesson that pertains most when times are difficult, when dangers abound, and when we some seek to drive us more by fear than by hope.

Or, as Franklin put it at the signing of the Declaration, We must all hang together, or assuredly we shall all hang separately.
Though Thomas jefferson did write the declaration based on some existing documents, there was a good deal of argument over how to (or whether to) say, “No thanks, we prefer not to” to the British. The new Adams bio does a nice job of laying out the facts.
Interestingly, the Declaration of Independence was actually ratified on the 2nd of July (a day close to my heart), and John Adams believed that that day would be celebrated as our Independence Day. However, it took two days for the document to be copied (Xerox not yet in existence), and the doc was signed on the fourth (although some argued for backdating), ergo the 4th of July.
Good points, all. Something like this had never really been done before, and it was a huge step to take.
If I had time today, I’d watch my copy of 1776 …