In "To Kill a Mocking Bird," Jem and Scout are greeted warmly during their visit to First Purchase Church. It is during this visit that Scout learns that Tom Robinson has been accused of rape by Bob Ewell. Scout witnesses the gentle determination of the black community to live peacefully and positively, even in the face of poverty.
The visit to the black church marks a point in the story where Scout sees the black community for herself. The community is hopeful and kind, rallying to support the wife of Tom Robinson since no one will hire her because he has been accused of raping a white woman.
Scout doesn't seem to understand how the white community would believe the accusation made by Ewell, a mean drunk who is essentially "white trash" in the community. The visit is a contrast to the later experience the children have with the white lady missionaries, who are willing to raise money for Africans but who talk disparagingly about the blacks in their own town.
The differences between the black community and the white community are used to show how racism can taint the vision, particularly when a quiet, respected member of the black community is accused of committing a crime against a woman of known bad reputation in the white community.