The final statement of Atticus Finch about people returns to his early remark to Scout to not judge people without getting to know them (Ch.3):
"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."
For, little Scout tells her father about a character in The Grey Ghost, but metaphorically, the character to which she refers is Boo Radley as she describes him, "Atticus, he was real nice."
Atticus replies, "Most people are, Scout, when you finally see them." Atticus recognizes that Scout has certainly matured now that she demonstrates that she understands what it is to "walk around" in someone's skin.
The last thing that Atticus says in the story is this:
“Most people are, Scout, when you finally see them.”
Atticus is responding to Scout's summarizing of events in the story of The Grey Ghost. In it, a boy is falsely accused of doing nasty things, because he is unfamiliar to a lot of people. Scout then tells Atticus that the people realized that the boy was actually very nice. Atticus replies with the above quote. The reader is meant to infer that Scout and Atticus are talking about the boy in the story and Boo Radley at the same time. Scout and Jem had thought Boo was the source of all kinds of neighborhood horror, but their opinions about Boo finally change at the end of the story. He saves them from Bob Ewell, and they meet Boo face to face. Scout realizes that he isn't scary or evil like they once thought. Scout now "sees" Boo Radley as he really is.