Read the excerpt from Narrative of the Life of Frederick Douglass. In the same book, I met with one of Sheridan's mighty speeches on and in behalf of Catholic emancipation. These were choice documents to me. I read them over and over again with unabated interest. They gave tongue to interesting thoughts of my own soul, which had frequently flashed through my mind, and died away for want of utterance.
In this excerpt, what effect does the adjective "mighty” have that the adjective "great” would not?

“Mighty” shows that Sheridan’s speeches are longer than most “great” speeches.
“Mighty” reflects how powerful and influential the speeches were to Douglass in a way that “great” would not.
“Mighty” and “great” mean essentially the same thing, so there is not much difference in their effect.
“Mighty” reflects a harsh bitterness that would not be reflected with the word “great.”