In chapters 3 and 4 of "To Kill a Mockingbird," what lesson does Calpurnia try to teach Scout about Walter?

Calpurnia tries to teach Scout that Walter was a guest in her home, and just because he is of a lower class, he is not to be treated as such. Calpurnia wants to make it known that a guest is to be treated cordially no matter what their social or economic class, and it is up to the host to make them comfortable.Calpurnia lets Scout know that it is wrong to try to point out a guest's behavior as inappropriate. This is evident when Walter pours syrup all over his lunch, and Scout embarrasses him by laughing out loud. Scout does not understand why it is not acceptable, as it is just "Walter" and he is a "Cunningham". Calpurnia tells her she was the one in the wrong, not Walter.Scout is punished for being impolite and is kept in the kitchen for the remainder of the meal.

Scout later complains to Atticus of Calpurnia's grievous error in punishing her, but Atticus not only supports Calpurnia, but reinforces the lesson as well.