What is the significance of Lee's portrayal of Calpurnia as she comes into the courtroom and as she walks home with the children?

Calpurnia isn't merely hired help for Atticus. The whole town is aware that Calpurnia is a mother figure to the Finch children. Calpurnia represents a rare bridge between the void of ethnicity. She and the Finch kids are a public display of a family that is truly enlightened.