Going to church in the black community is a time for everyone to present his/her best self. It is an important social affair where women wear hats, and people wear their finest clothes. The night before church, Calpurnia gives Scout and Jem a bath, scrubbing them to make sure they are clean. She sets out their Sunday clothes and makes sure they are ready to go with her on time. The children’s cleanliness and the way they are dressed is a reflection on Calpurnia’s ability to take care of the children of her employer. Dressing up for church is also a sign of respect that Calpurnia wants to make sure the children show. She knows that this will be a new experience for the children and Calpurnia wants to make sure they are respectful and presentable to the congregation. Calpurnia may also fear some backlash from the congregation, like she does when Lulu says to Calpurnia that “You ain’t got no business bringin’ white chillun here—they got their church, we got our’n." Scout and Jem’s reception at the church is a little cold, and, at first, it is questioned by the congregation until Reverend Sykes and Zeebo welcome them to the service. It is ironic that the black church in Maycomb is so welcoming because a white church in Maycomb would never embrace black children attending their services.
In my opinion, Calpurnia wants the kids to look nice before she brings them to her church because she thinks a couple of things.
First I think she thinks that the way they look will reflect on her. She thinks that if they look bad it will seem that she does not take care of them well.
Second, I think that she does not want them to show up at her church looking bad because it will make it look like they, as white kids, do not respect the black church enough to dress up.