What did Atticus hope to teach Jem by making him read to Mrs.Dubose?

Atticus warns Jem to be a gentleman to her, because she is old and sick, but one day she tells the children that Atticus is not any better than the “niggers and trash he works for,” and Jem loses his temper. Jem takes a baton from Scout and destroys all of Mrs. Dubose’s camellia bushes. As punishment, Jem must go to her house every day for a month and read to her.