Answer:
Essentially, Douglass uses the Fourth of July, when Americans celebrate their independence and their freedoms, to illustrate what he says is the "immeasurable distance" between enslaved people and the rest of Americans. He juxtaposes the ideals of America, celebrated on the Fourth, with the reality of slavery. He must have felt relieved and glorious about it.
The correct answer is invoke a curse or judgment.
They were used to invoke the wrath of god upon your enemy.
