What is the lesson that Scout learns from Calpurnia at lunchtime?

Walter Cunningham comes over for lunch. Scout watches him eat and is appalled by his manners and eating habits:

Walter interrupted to ask if there was any molasses in the house. Atticus summoned Calpurnia, who returned bearing the syrup pitcher. She stood waiting for Walter to help himself. Walter poured syrup on his vegetables and meat with a generous hand. He would probably have poured it into his milk glass had I not asked what the sam hill he was doing (Chapter 3).

Scout starts to protest. She cannot believe someone would want sweet syrup all over their savory food. Calpurnia interrupts Scout and calls her to come in the kitchen.

Once in the kitchen, Calpurnia scolds Scout.  She is very mad at Scout for calling attention to a guest's manners. She reminds Scout several times that Walter Cunningham is a guest in their house and should be treated with respect. Scout tells Calpurnia that Walter is not really a guest, but Calpurnia is firm. She tells Scout that anyone who comes into their house is considered a guest. Lastly, she tells Scout that she will have to eat in the kitchen instead of at the dinner table unless she behaves herself.