In To Kill a Mockingbird, what does Jem notice about the way Calpurnia speaks at church?

In Chapter 12, Calpurnia takes Jem and Scout to First Purchase African M. E. Church. It is the first time the children visited an African American church, and they gain valuable insight into the black community of Maycomb. Later on the chapter, Calpurnia explains how she taught her son Zeebo to read using Blackstone's Commentaries. Jem is awestruck because Blackstone's Commentaries is a very challenging book to read. He says to Calpurnia, "That's why you don't talk like the rest of 'em...Rest of the colored folks. Cal, but you talked like they did in church..." (Lee 167) Jem and Scout both notice that Calpurnia speaks differently around her community members. Calpurnia speaks informally and uses a Southern African American dialect that is typical of that region during the early 1900's. Scout mentions that Calpurnia lived a "modest double life" and has "command of two languages." Calpurnia explains to the children that if she talked formally then her neighbors would think she was "puttin' on airs to beat Moses." (Lee 167) Calpurnia tells Scout that it's not lady-like to tell people all you know, and that people don't like being around others who know more than they do. Scout and Jem learn important lessons in manners and human relations on their visit to Calpurnia's church.