One of the most famous metaphors in Harper Lee's To Kill a Mockingbird is said by Atticus to Scout early in the novel. In Chapter 3, after Scout has had a very disappointing first day of school, Atticus uses a metaphor to teach Scout the principle he lives by of understanding, accepting, and respecting other people:
You never really understand a person until you consider things from his point of view-- ... --until you climb into his skin and walk around in it. (Ch. 3)
Scout takes this message very much to heart, and it comes up several other times in the book. By the final chapter of the novel, Scout has grown enough that she can reword the metaphor on her own:
One time [Atticus] said you never really know a man until you stand in his shoes and walk around in them. (Ch. 31)
Scout recalls Atticus's lesson in understanding and accepting others as she stands on the porch of Arthur Radley and sees the neighborhood through his eyes. As she does so, she thinks about how Arthur observed the activities of "his children" with feelings of generosity, care, and even concern.
Another important metaphor is spoken by Atticus to Jem and helps develop the theme concerning courage. Jem has just had his experience with Mrs. Dubose in which he learns to see her as not just a cantankerous, hateful old woman but as a truly great lady due to her bravery. Atticus had wanted Jem to spend time reading to Mrs. Dubose with the express purpose of teaching him the true meaning of courage. Atticus uses a metaphor to explain what he wants Jem to see courage as being:
I wanted you to see something about [Mrs. Dubose]--I wanted you to see what real courage is, instead of getting the idea that courage is a man with a gun in his hand. (Ch. 11)
Atticus continues to explain that he wanted Jem to see courage as the ability to undertake a task one is unlikely to succeed in but following through with it regardless, simply because one knows it is the right thing to do, a message that is a central premise of the book.