Atticus has a very strong sense of morality that he instills in his children. He teaches them by example, and several times in the novel he speaks to them directly about moral behavior. He explains for instance, why he is defending Tom Robinson:
This case, Tom Robinson's case, is something that goes to the essence of a man's conscience . . . I couldn't go to church and worship God if I didn't try to help that man.
Atticus continues to explain:
. . . before I can live with other folks I've got to live with myself. The one thing that doesn't abide by majority rule is a person's conscience.
As Jem and Scout watch their father treat others with respect (including Mrs. Dubose), take on Tom's case, stand up to a lynch mob, protect the Radleys' privacy, refuse to let Alexandra demean Cal, and explain the nature of mockingbirds, his moral lessons become a part of their characters, which is easily observed as they grow up. Jem cries when Tom is convicted, and Scout reaches out gently to Boo, understanding his feelings and anticipating his needs as she takes his hand and walks him home at the conclusion of the novel.