On Wednesday, Barack Obama will deliver one of the most important speeches of his presidency. He will be standing in the shadow of Abraham Lincoln, 150 years after the Gettysburg Address, on the steps where Martin Luther King delivered his immortal “I Have a Dream” speech exactly 50 years before. The president has been criticized at times for responding to every crisis by giving a speech, with words rather than action. But as both the Gettysburg Address and the “I Have a Dream” speech show, words can have enormous power.

Sometimes, a speech can change history. Consider the Gettysburg Address. Delivered on the site of the transformational battle in the bloodiest war fought on U.S. soil, President Lincoln declared this nation to be one that was “conceived in liberty and dedicated to the proposition that all men are created equal.” In a mere 272 words, his address, in the words of historian Garry Wills, “remade America.” Lincoln’s short speech paved the way for the adoption of the Reconstruction Amendmentsafter the War ended. These amendments—the 13th, 14th, and 15th—ended slavery in the United States, enshrined equality in our nation’s charter, and secured the right to vote for African-American men.

But just as the work of those who fought at Gettysburg was left unfinished, so too was President Lincoln’s. One hundred years later, the nation was still in the throes of the ugliness and terror of Jim Crow and the violations of the letter and spirit of the Reconstruction Amendments.

A great task remained before this country, as Dr. King walked up the steps of the Lincoln Memorial to deliver one of the most famous speeches of the 20th Century. King declared that he had come to Washington to “cash a check,” and to make good on the “promissory note to which every American was to fall heir.” This promissory note, King said, was evident in “the magnificent words of the Constitution and Declaration of Independence.” This check to cash, this promissory note, are the guarantees of the 13th, 14th, and 15th Amendments. In 1963, America was still defaulting, and failing to “honorthis sacred obligation.”

The task before President Obama is not near as great as the ones facing Lincoln or King — we are not in the midst of a Civil War, nor does de jure apartheid exist in half of our country. But this is an important moment nonetheless. Unfinished business remains on our way to a “more perfect union” and achieving Dr. King’s dream of transforming this nation “into an oasis of freedom.” Our nation still confronts the profiling of people of color. For too many Americans, “lonely island(s) of poverty” offer little hope for achieving an American dream. The incarceration rates of African-Americans remain unconscionably high. And even voting, that most sacred of democratic actions, is under threat.

Two months ago, the Supreme Court in Shelby County v. Holder struck down a key part of the Voting Rights Act (VRA), one of the singular legislative achievements of the past century. The Court did so despite overwhelming evidence – including the text of the Constitution itself — that the framers of the 15th Amendment trusted Congress, not the Court and certainly not the States, to protect the franchise, and in spite of significant evidence that efforts to disenfranchise voters are still alive and well in this country.

As the Shelby County ruling makes clear, there is a battle raging in this nation over the meaning of the Reconstruction Amendments. For the conservative majority on the Supreme Court, the progress made over the last 50 years supports their ruling gutting a key part of the VRA. But asJustice Ginsburg put it in her dissenting opinion, this is like “throwing away your umbrella in a rainstorm because you are not getting wet.”

This is where President Obama can make his mark next week. It is unlikely that Americans will remember President Obama’s words 50, much less 150, years from now, but President Obama can work to transform the current debate about civil rights in America. To do so, like King and Lincoln, he must do more than describe the problem; he must harness the power of the text and history of the Constitution and its Reconstruction Amendments in service of his attempt to address our nation’s lingering inequalities.

When he makes his remarks next week where Dr. King gave his ringing oratory, and just yards from the words of the Gettysburg Address immortalized in the marble of the Lincoln Memorial, President Obama should use this momentous anniversary as an opportunity to affirm our nation’s commitment to the promises of equality and voting rights as guaranteed by the words of the United States Constitution.