The line that supports Douglass’s claim that the Fourth of July is not a cause worthy of celebration for all is:
"Fellow-citizens, above your national, tumultuous joy, I hear the mournful wail of millions! whose chains, heavy and grievous yesterday, are, to-day, rendered more intolerable by the jubilee shouts that reach them."
This line highlights the contrast between the celebration of independence by some and the continued suffering of enslaved individuals, emphasizing that the joy of the Fourth of July is not universally experienced and suggesting that it is a painful reminder of the ongoing oppression faced by millions.