At the novel's conclusion, Scout walks Boo Radley to his front door, where he turns the doorknob and goes inside, never to be seen again. As she stands on his porch, Scout's more mature perspective is evident in her reflections:
Neighbors bring food with death and flowers with sickness and little things in between.
Since the Finch family is traditionally Methodist, Scout is likely aligning her views of being a true neighbor with the commandment found in Mark 12:31: Love your neighbor as yourself. These acts which Scout attributes to being neighborly also show compassion and concern—or love. Neighbors try to lighten each other's burden when hardships arise. They try to brighten each other's worlds with small tokens of beauty.
Boo has done this for Scout:
Boo was our neighbor. He gave us two soap dolls, a broken watch and chain, a pair of good-luck pennies, and our lives.
Boo has gotten to know these children without ever interacting with them. He intentionally tried to bring joy to their lives by leaving small gifts for them, those small tokens of beauty which make the world a little brighter. But Scout also realizes now that "neighbors give in return." Though Boo has come to love his neighbors, risking his own life to save theirs from the evil Bob Ewell, the children have never reached out to Boo in love. Instead, Atticus describes their interactions earlier in the book as "tormenting" the man.
This realization pains Scout. While a man with few resources and almost no interaction with society found a way to show love to Scout and Jem, they have never reciprocated these small acts of love. She now understands that being a "good" neighbor involves compassion, intentional acts of service, and, most of all, love.