Atticus speaks about the necessity of looking at things through someone else’s eyes. This is a lesson that Scout has to learn the hard way in her dealings with other children at school and with other people in general.
The actual quote I’m referring to is:
"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."
Scout, as a first grader, has a difficult time applying this to people like Walter Cunningham, Miss Caroline, Calpurnia, and other characters. But near the end of the story we see that she had learned this lesson after all, when she says that Atticus was right about it. At that time she’s referring to Boo Radley and the fact that she can finally see things from his point of view.
Harper Lee uses this as a unifying aspect of the novel by establishing it early and then referring to it again near the end in the same words. It shows how Scout has grown and the value of Atticus’ teaching.