Brief Summary
The Set-Up
Frederick Douglass, a former slave and accomplished orator, gave this speech to the citizens of Rochester, New York, during their Independence Day celebration on July 4th, 1852.
The Text
Douglass starts by pointing out to the audience that asking a former slave to speak on Independence Day, a holiday that celebrates freedom, is pretty weird. After all, can slaves celebrate freedom? Uh, no. Is this some kind of sick joke?
The only way Douglass can reconcile speaking at a celebration of American freedom is to speak about American slavery, so that's what he does. He points out all the ways in which it is seriously messed up for white Americans—even abolitionists—to celebrate their own freedom while people are held in bondage. He points out how hypocritical it is to celebrate the nation's freedom while the nation is actively false to those ideals.
Then, Douglass brings up all the arguments he's not going to make about slavery. He essentially says, "Come on, guys and gals, you know it's ridiculous to argue that slaves are people, too, when obviously slaves are people, too."
He finishes up the speech by repeating his earlier assertion that celebrating freedom while slaves are held in the United States is hypocritical, and he goes on to say that really, celebrating the Fourth of July just makes the United States look even worse than it did before.
Mic drop.
TL;DR
Douglass says that celebrating the Fourth of July while slavery is still legal is ridiculous and cruel in a whole lot of ways.