At breakfast the next morning, the day of the trial, Atticus says that Mr. Underwood never liked black people, which makes his behavior of the previous night seem odd to Scout.
Underwood did what's right even though he's a racist. Like Mrs. Dubose, Underwood fought against himself and won.
Jem declares Mr Cunningham would have killed Atticus the previous night. But Atticus says Mr. Cunningham just has his blind spots like everyone else, and is still a friend.
Atticus respects the dignity of people who meant to harm him.
People from all over Maycomb head for the courthouse, including some Baptists who quote the bible condemning Miss Maudie Atkinson for keeping a garden. She quotes a bible verse right back at them which proves her garden is actually beautiful in God's eyes.
The baptists condemn Miss Maudie just for enjoying flowers! Intolerance is made to look ridiculous.
Though Atticus tells Jem, Scout, and Dill that they shouldn't attend the trial, they sneak in. They arrive late, and can only find seats in the balcony where the black people have to sit. Judge Taylor is presiding, and Heck Tate is already on the stand.
The black people welcome Jem, Scout, and Dill, though the white people are not welcoming of blacks and segregate them in the balcony.