When we celebrate Martin Luther King Day on Monday, many of us will remember him first as a great preacher and a powerful speaker.

His majestic address from the steps of the Lincoln Memorial remains, almost 50 years after it was delivered, the greatest achievement of American oratory since the Gettysburg Address.

When King shared his dream that “one day the sons of former slaves and the sons of former slave owners” would be able to “sit down together at the table of brotherhood,” his words moved the hearts of the multitude on the National Mall and stirred the nation’s soul to embrace the cause of civil rights.

Some of that oration’s power came from the skillfulness of King’s delivery.

He was, first and foremost, a minister and a preacher, trained in a Baptist tradition that valued evocative preaching. Someone who understood nothing about King’s words but heard only the sound of his preaching voice would feel and know immediately how to respond.

As the words and occasion demanded, King made of his voice a trumpet for justice, a storm of thunder against oppression and a song for joy at heaven’s peace.

More of the oration’s power derives from the artfulness of its composition. To study the text of the “I have a dream” speech is to take a master’s course in the use of rhetorical devices and figures.

Like any great writer, King knew when to borrow. The “dream” speech opens with an allusion to the Gettysburg Address, ends with the chorus of a spiritual hymn, and in between we hear echoes of Shakespeare, strains of patriotic song, and of course, the psalms, the prophets and the gospel.

And he knew when to break the ordinary rules of writing for extraordinary effect. He knew when to use the catachresis: the device of using an unexpected word to create a powerfully paradoxical picture in the reader’s mind — he spoke of “soul force” and “creative suffering.”

He knew when it was right to use the wrong part of speech to compose an anthimeria, as he does when he evokes the “fierce urgency of now.”

And King knew the power that figures of repetition impart to a speech meant to be heard more than read. We remember the speech for the words “I have a dream” because he repeats them nine times, to structure and frame his vision, so that we could see it clearly and remember.

Had King’s address that day in 1963 been just a brilliantly delivered rhetorical showpiece, we would not remember it today.

The most important part of any persuasive speech or writing is its argument, and King that day articulated the case for integration and civil rights in terms at once simple and compelling. And by grounding his dream “in the American dream,” he forced his opponents to see that they could only live up to their own ideals by recognizing the justice of his demands.

At our nation’s birth, he argued, our founding father’s made a promise: They promised to build a nation dedicated to the proposition that all men are created equal and endowed by their creator with unalienable rights.

In the early days of our republic, however, that promise was only kept for a few. When Lincoln spoke at the Gettysburg cemetery while the Civil War still raged, he recalled that promise, and called for the fulfillment of that promise and for a new birth of freedom.

But after Lincoln’s death, the infant promise freedom was strangled in its crib.

King spoke a century after Lincoln’s address, to demand that the old promise finally be kept. He had come to the capital, he said, to redeem the “promissory note” contained in the Declaration of Independence.

Though America had till then defaulted on her obligation, King refused to believe that the “bank of justice is bankrupt.”

It was his dream that this nation would “rise up and live out the true meaning of its creed: ‘We hold these truths to be self-evident, that all men are created equal.'”

It was his dream that “all of God’s children, black men and white men, Jews and Gentiles, Protestants and Catholics,” would be united one day in a joyous song of freedom.

Though that day has not yet come, King’s great speech and his work have brought it closer by proving why all true Americans should constantly labor to bring that day ever closer.

Joseph R. Reisert is associate professor of American constitutional law and chairman of the department of government at Colby College in Waterville.