Explain the proper use of the comma to set apart nonessential elements within a sentence

Read these excerpts. lincoln's "gettysburg address." it is for us the living, rather, to be dedicated here to the unfinished work which they who fought here have thus far so nobly advanced. whitman's "o captain! my captain! ". exult, o shores, and ring, o bells! but i, with mournful tread, walk the deck my captain lies, fallen cold and dead. which rhetorical appeal do both excerpts use? logos: the use of logic to convince the audience pathos: the use of emotional appeals to affect the audience’s feelings brevity: writing or speaking that is short, brief, and to the point ethos: the use of authority to persuade the audience to act the right way