Brief Summary
The Set-Up
Slavery existed and women didn't have the vote in the first half of the 1800s. The people who weren't complete dirtbags wanted to change that…and had conventions to build up followers.
The Text
Truth begins her speech by pointing out that women and Black men gathering together should strike terror in the hearts of men attached to the status quo. (So you know this is going to be good.)
The status quo is that women need to be protected, and she describes all the special treatment that she never receives. Yeah; both of these are messed up. Women aren't fragile things that need to be treated like weird glass-blown angels…Sojourner Truth proves this by being strong.
…but she also proves that Black women are treated absolutely horrifically. She gets worked like a man (and beaten like a man) and so is considered less of a woman and less of human being.
Then she brings up the complete lack of logic present in inequality. She—being Black and a woman in the 1800s—is allowed less than a white man. But white dudes are getting snippy because she's asking for just a little more in the way of rights. Why are these guys getting miffed, exactly? She's not asking for them to have fewer rights than they already have; she's just asking for more than what she has.
Some of these dudes argue that women can achieve less because—check out this skewed logic—Jesus was male. Truth states that this is ridiculous. After all, God depended on Mary to bring Jesus to the world.
And speaking of Biblical women achieving Big Deal things: Eve managed to turn her world upside down with just one bite of an apple. So a statement that women can't get things done is insane: with the combined forces of determined women, there can be change again. Eventually, men will bow before the force of women's power.
Now that's how you end a speech.
TL;DR
A Black woman stood up and said, "Hey, I'm human, too. And I deserve just as many rights as Black men and white women."
And then the sound of her dropping the mic echoed through history.