The hard-boiled realist who wrote that “few members of the oppressor race can understand the … passionate yearnings of the oppressed race” must have scoffed at the dreamer who divined the day when black and white children would join hands as brothers and sisters. In truth, Martin Luther King Jr. made both statements: the first, in the “Letter From Birmingham Jail” four months before he soared majestically with the second at the March on Washington. Recognizing the Christian warrior who lingers in the shadows of the “I Have a Dream” speech is critical: To strip the “Dream” of its righteous edge betrays the very meaning of King’s ministry.

In the “Letter,” King entertained no illusions that soaring rhetoric alone could stir the conscience of whites. “Freedom,” he declared, “is never voluntarily given by the oppressor; it must be demanded by the oppressed.” The indignant prophet warned, “We will have to repent … for the appalling silence of the good people.”

If the “Letter” was fiery mad, the “Dream” was fiery glad. At least that was true of the passages Americans are keen to remember. King celebrated “the magnificent words of the Constitution and the Declaration of Independence” that day 50 years ago in Washington. He offered wondrous dreams — the children of former slaves and slave owners sitting “at the table of brotherhood.” He rang the chimes of freedom and gave a foretaste of freedom’s coming: “We are free at last!”

Yet none of this extinguished the black pride and defiance that had energized the “Letter’s” bristling prose. King embraced “extremism” in the “Letter”; in Washington, he reveled in “marvelous new militancy” and trumpeted “the fierce urgency of now.” Imagining a white questioner asking, “When will you be satisfied?” he replied with an irrepressible black “we”: “(N)ever … as long as our children are stripped of their selfhood and robbed of their dignity …” The final condition — “(W)e will not be satisfied until justice rolls down like waters” — intimated the prophetic judgment that hovered over both “Dream” and the “Letter.”

Despite the imagery of “American dream,” King’s shout-out to the “Negro slaves who had been seared in the flames of withering injustice” signaled that he would read American history as an alienated outsider. A century after the Emancipation Proclamation, “the Negro (still) … finds himself an exile in his own land.”

King’s efforts to speak from within the American tradition testified not to the nation’s greatness but its failure to achieve it. Staking out a claim to black ownership, he invoked the “architects of our republic.” He tinkered with Jefferson’s words, turning them into an accusation: The founders had signed “a promissory note … that all men,” — here he borrowed from Frederick Douglass — “‘yes, black men as well as white men’ — would be guaranteed the unalienable rights of life, liberty and the pursuit of happiness.” But America had “defaulted on this promissory note.” To affirm the declaration, King had to rewrite it.

The second half of “I Have a Dream” was not as tough as the first. And yet the chiding was simply submerged, carried along by implication. King’s dream that “my four little children will one day live in a nation where they will not be judged by the color of their skin” declared that they did not live there yet.

Four months earlier, King had been more explicit about how to arrive at that future. Fresh from his jail cell, he preached a remarkable version of the “Letter” to a black audience at 16th Street Baptist Church that previewed the ending of his Washington speech. “Let freedom ring!” King commanded, from “every hill and molehill in Mississippi.” Deliverance depended not on the goodwill of whites but on the actions of blacks:

If we will stick together,

If we will pray together,

If we will work together,

If we will protest together,

We will be able to bring that day.

We will be able to bring that day!

That’s a good guide to how we should commemorate “I Have a Dream,” and all the events of that spring and summer. Not with self-congratulations about how far we’ve come or faith in the destiny of American democracy. Nor with hero worship of a mythologized Moses as if he alone led his people out of bondage with his golden tongue. If blacks or whites were to be able to sing “America, my country ’tis of thee, sweet land of liberty,” as King imagined at the March on Washington, the civil rights movement would first have to “bring that day” — through struggle, civil disobedience, bloody sacrifice and even death. In short, the nation most white Americans thought they lived in would not exist until black people created it.