Next Wednesday, August 28th, will mark the fiftieth anniversary of Dr. Martin Luther King’s “I Have a Dream” speech. Now regarded as one of the greatest flights of public oratory in American history, the speech, delivered from the steps of the Lincoln Memorial on the National Mall, was the culmination of the March on Washington for Jobs and Freedom, an event that mobilized nearly a quarter of a million citizens on behalf of civil rights.

We remember the speech for its prophetic closing paragraphs, in which Dr. King voices his vision of an America vibrating with racial harmony, as opposed to discord. But for the majority of the white population of Washington, D.C., the gathering of hundreds of thousands of angry black people, bused in from every corner of the land — some of them avowedly “militant” — was not exactly a cause for celebration.

In fact, the coverage in the Washington Post the following day had more of the character of a police report than a political analysis. Dr. King’s speech wasn’t singled out for any particular plaudits. Mainly, the city seemed relieved that the rally hadn’t ended in the kind of violence that many had predicted: an eruption of rage, looting, and blood-letting.

In retrospect, the speech is masterful in the way it looks to the future through the lens of history; the way it honors the crowd’s anger, but channels, rather than stokes, it; and appeals to the best impulses of the American people, white and black, rather than the worst.

The word “freedom” blazes an incandescent trail through its pages, but what does Dr. King mean by it? What, exactly, is the freedom he dreams of, the kind that will ring from the mountaintops, that will cause the American people to join hands and sing ecstatically, “Free at last!”

Freedom from what? Freedom to do what?

Freedom from injustice, certainly. Freedom to pursue the American Dream.

For Dr. King, the American Dream is rooted in what he calls its creed: “We hold these truths to be self-evident, that all men are created equal.”

He says this knowing all too well the irony in those sacred words from the Declaration of Independence. The men who wrote them didn’t really believe that men were created equal. Many of the Founding Fathers owned slaves. And slaves weren’t created equal. You couldn’t own someone who was your equal; therefore, slaves weren’t men. At least, not fully. A slave was some fraction of a man. Call it three-fifths.

But those imperfect, 18th Century men were dreamers, too. They invented a country that promised more than it could deliver. They drew up a constitution with the goal of forming a more perfect union — not a perfect union, mind you, but a more perfect union. They understood that we live in the world; that the world is full of injustice, greed, and cruelty; that people generally want to do the right thing, but aren’t always strong enough to do it.

Ours has been a history of forgetting our promises, then remembering, and lurching, sometimes violently, towards the light.

Even some of our greatest triumphs have fallen short. Take the Emancipation Proclamation. Church bells rang out across the land on January 1st, 1863. Freed slaves and abolitionists alike were overjoyed. Surely there were ecstatic cries of “Free at last!”

But the Emancipation Proclamation didn’t free all the slaves. President Lincoln couldn’t risk losing the border states. The slaves in Maryland, Delaware, and Kentucky may have heard distant ringing that day; alas, the bells weren’t ringing for them.

The century that followed the Emancipation Proclamation saw many gains for people of color, but also great backsliding. In states like Mississippi, Georgia, and Alabama, equality wasn’t simply an impossibility; in huge swaths of the country, it was no longer even a dream.

Dr. King’s speech, smoldering with anger and yet brimming with hope, was meant to remind Americans of their creed, that promise of equality dating back to the Declaration of Independence.

Our union is certainly more perfect now. The scourge of slavery is long past. The worst abuses of Jim Crow are over.

But their legacy remains.

We’ll always need voices like Dr. King’s — righteous, melodious, idealistic, and stern — to remind us of the nation we were; the nation we are; and the nation we hope to be.

History shows us how easy it is to forget.