This passage is significant as it draws attention to the thematic concerns of Harper Lee's novel; namely, the social inequities of Maycomb, Alabama, in 1935.
The sensitive Dill, who identifies with Tom as an underdog also, begins to cry sympathetically when he witnesses the cruel and demeaning manner of the prosecutor, Mr. Gilmer, who harshly interrogates Tom Robinson. Consequently, Scout escorts Dill outside, where Scout explains Mr Gilmer's words and tone are as consistent with any prosecutor's. Besides, she adds, Tom is "just a Negro."
Scout's words typify those of many who listen to the trial, and Dill is not satisfied with them. Before he can attempt to articulate his feelings, however, Mr. Dolphus Raymond answers for him, saying, "...it just makes you sick, doesn't it?" He means that things do not seem fair to Tom Robinson, who has done nothing but try to help a girl who is on her own most of the time.
Mr. Raymond tries to cheer up Dill by saying of Tom that "Things haven't caught up with that ones' s instinct now." But, in actuality, Dill sees Tom's situation realistically and knows that the boy is in serious trouble.