Answer:
He was in Gettysburg to dedicate a national military cemetery to the Union soldiers who fell at the Battle of Gettysburg four months earlier. Lincoln goes back in time—not to the signing of the Constitution, but to the Declaration of Independence.
The best summary of the excerpt is Pangu Grew
He hears the cries of suffering from the humans.
The trustworthiness of a speaker adds to the speaker's "appeal to reasoning" although it should be noted that it also contributes to the speaker's reputation.
