What did Lula say to Scout, Jem, and Calpurnia at the church entrance? What did Calpurnia say back? Why did she change her voice, like how the blacks say it?

A black woman named Lula tries to tell Calpurnia that white children don't belong at the church. However, Calpurnia points out that it's the same God, and the rest of the congregation welcomes the newcomers. Scout is surprised to hear Calpurnia speak in the same black dialect as the others, because at home, Calpurnia always speaks proper English.

Calpurnia's ability to speak both the English of the white community and of the black community shows one aspect of her role as a mediator between the otherwise far-removed worlds of black and white. She is often called upon as a go-between between the two communities, as in the case of the death of Tom Robinson in chapter 24. She manages to bridge both worlds without becoming a foreigner to both, as in the case of the "mixed" children seen around the courthouse in Chapter 16. However, the discussion of English dialects also dates Lee's book considerably, as white grammar is referred to as "proper" English, whereas black grammar comes across as being a more ignorant way of speaking. More recent linguistic research has demonstrated that the dialects of African-American English follow the same logical, systematic rules as all languages and are correct and perfectly contained unto themselves. Calpurnia explains that members of the black community prefer to speak their own form of English, which shows that their dialect helps to identify them as a group, an idea which has contemporary reverberations with respect to the issue of introducing Ebonics in American public schools.

Ignorant.