It was on July 5, 1852, that Frederick Douglass addressed the Ladies’ Antislavery Society in Rochester, N.Y., and delivered what is often described as the greatest abolitionist speech in US history. “What, to the American slave,” Douglass demanded of his audience, “is your Fourth of July?”

It was not by happenstance that Douglass gave his renowned July 4 speech on the day after July 4. He had insisted on it. Ever since slavery had been abolished in the state of New York decades earlier, Black New Yorkers had celebrated their emancipation on July 5. The date was chosen both as a symbol of the independence still denied to those enslaved in 15 other states and the District of Columbia, and as an acid comment on the fraudulence of a nation that commemorated its liberty with parades and fireworks while permitting and enforcing the chattel slavery of African Americans.

So when Douglass stipulated July 5 as the date for his speech, his audience likely anticipated that he would be scathing in his denunciation of that grotesque double standard. He didn’t disappoint.

With the wrath of an Old Testament prophet, Douglass declared that “from the slave’s point of view,” the Fourth of July more than any other day underscores the “gross injustice and cruelty to which he is the constant victim.”

Douglass, who had been born into slavery and escaped as a young adult, vented his moral outrage.

“Your celebration is a sham; your boasted liberty, an unholy license; your national greatness, swelling vanity,” he declaimed. “Your prayers and hymns, your sermons and thanksgivings, with all your religious parade and solemnity, are … mere bombast, fraud, deception, impiety, and hypocrisy — a thin veil to cover up crimes which would disgrace a nation of savages. There is not a nation on the earth guilty of practices, more shocking and bloody, than are the people of these United States, at this very hour.”

Douglass’s speech is widely anthologized and reprinted; students are often assigned to read it; and it can be heard in numerous online recordings, with Douglass’s words recited by everyone from acclaimed actors to the great man’s own descendants. But because the speech is very long — nearly 10,500 words — it is rarely presented in full. Instead, readers and viewers are apt to get only highlights of what Douglass said that day, primarily his scorching attacks on the duplicity that kept slavery alive.

Yet as memorable and eloquent as those passages are, they were not the core of his message. Douglass excoriated America’s hypocrisy. But he exulted in America’s democratic promise. He placed his faith in the principle of equality and justice enshrined in the Declaration of Independence and the Constitution. He had come to Rochester not to damn white Americans but to implore them to live up to the Founders’ highest ideals. Many years later, Martin Luther King Jr., speaking to a vast throng at the Lincoln Memorial, would make a similar argument.

But it was Douglass who made the argument first. And in doing so, he was rejecting the view of some of the towering abolitionists of his time, including his own mentor, hero, and former ally, William Lloyd Garrison, of Boston.

In his lectures and his influential newspaper, The Liberator, Garrison preached that the Constitution was an evil document, a deal with the devil that protected slavery and with which there could be no compromise. At one July 4 rally, Garrison burned a copy of the Constitution, calling it “a covenant with death, and an agreement with hell.” For years, Douglass had agreed with Garrison and regarded the American founding as having been corrupted from the start. He renounced any patriotism. As he told Garrison in 1846, any patriotic sentiment “was whipt out of me long since” by the slaveowners who had abused him in his youth.

But gradually Douglass changed his mind. He began “to re-think the whole subject,” he would later write in his autobiography. Eventually he concluded that Garrison and his disciples were wrong. The Constitution was not a pro-slavery document. It was fundamentally anti-slavery. Even when it referred to slavery, as in the notorious Three-Fifths Clause, it did so obliquely, employing embarrassed euphemisms and speaking only of “persons,” never of slaves.

“Take the Constitution according to its plain reading,” Douglass told his Rochester audience, “and I defy the presentation of a single pro-slavery clause in it. On the other hand, it will be found to contain principles and purposes, entirely hostile to the existence of slavery.” The framers of the Constitution, far from permanently entrenching human bondage, had laid the groundwork for its uprooting. “Interpreted as it ought to be interpreted,” proclaimed Douglass, “the Constitution is a glorious liberty document.”

What was true of the Constitution was even truer of the Declaration. For all their sins — including, in some cases, the enslavement of fellow human beings — the signers of the Declaration were brave and wise men, Douglass said. “I cannot contemplate their great deeds with less than admiration. … And for the good they did and the principles they contended for, I will unite with you to honor their memory.”

What makes Douglass’s Rochester speech so remarkable is not his blistering anger at hypocrites who spoke of freedom while upholding slavery. It is his conviction that embedded in America’s charter documents were the principles through which slavery could be destroyed. At a time when leading antislavery activists regarded the American experiment as a failure and betrayal, Douglass saw in it reason for hope and optimism.

He spoke on the Fifth of July, but he nevertheless exalted the date atop the Declaration of Independence. “The Fourth of July is the first great fact in your nation’s history — the very ring-bolt in the chain of your yet undeveloped destiny,” Douglass told his listeners. “Cling to this day — cling to it, and to its principles, with the grasp of a storm-tossed mariner to a spar at midnight.” The great abolitionist rejected the counsels of despair and contempt. The American founding, he knew, was as relevant as ever, holding out the promise of greater, better days to come. It was so in 1852. It remains so today.