Most people have forgotten that at the civil rights march on Washington DC on 28 August 1963, Martin Luther King was not the featured speaker. He was not the icon of the movement that we think of today. He was a major player, yes, but there were others more famous, respected, and important at that time. The speech he gave—the one you know—changed that.
The importance of the speech is distinctively American. The United States, unique among nations, is a frankly artificial creation. France is the place in Europe where people speak French, but the US has no ethnic definition—this place is full of immigrants who decided to be Americans, and their children. Japan is an island, but there's nothing natural about the borders of the US—this place wound up a nation through a chaotic combination of war, purchase, legislative decisions, and (oh yeah) genocide. The US is an idea. Something we just made up.
This is why we have our peculiar veneration of documents. The Declaration of Independence and the Constitution are the holiest of holies in our civic religion because they are made of words, made of ideas. Through acclamation over the years we have chosen a handful of other documents that tell us what the United States is, like Lincoln's Gettysburg address and Martin Luther King, Jr.'s I have a dream speech. In that speech, the power of King's rhetoric and ideas was so great that hearing it transformed our understanding of what the nation was about. I know, I know, that's a white guy thing to say: it's not like plenty of folks didn't know about American racial injustice. But on the level of shared understanding of shared destiny, King gave dazzling voice to ideas implicit in the American national promise that had too long been denied. And still are denied today.
In a sense we have come to our nation's capital to cash a check. When the architects of our republic wrote the magnificent words of the Constitution and the Declaration of Independence, they were signing a promissory note to which every American was to fall heir.
This note was a promise that all men would be guaranteed the inalienable rights of life, liberty, and the pursuit of happiness. It is obvious today that America has defaulted on this promissory note insofar as her citizens of color are concerned. Instead of honoring this sacred obligation, America has given the Negro people a bad check which has come back marked “insufficient funds.” But we refuse to believe that the bank of justice is bankrupt. We refuse to believe that there are insufficient funds in the great vaults of opportunity of this nation.
Go read it right now. It will only take five minutes of your time. With no exaggeration, I think it's your duty as an American — we have a lot of work left to do.
And while you're at it, take a little more time and read Letter from a Birmingham Jail. I know you did it back in school. It's worth doing again.