It is Miss Maudie Atkinson who first explains to Scout about Atticus's belief that it's a "sin to kill a mockingbird." Maudie explains that mockingbirds do no harm to humans or their crops; instead, they are put on this earth to "sing their hearts out for us." Mockingbirds are small and innocent beings, and by the end of the novel, Scout recognizes that life provides tragic examples of human mockingbirds (Boo Radley and Tom Robinson), too.
Maudie is probably the most independent woman in the novel, and she is presented in a positive light by Scout, who considers her neighbor "our friend." Maudie is less of a gossip than Miss Stephanie and Miss Rachel, and Scout recognizes that most of the advice she receives from Miss Maudie comes from experience and not from second-hand neighborhood speculation. Maudie treats Jem and Scout as equals, never condescending to them and always addressing them by their proper names. Scout learns that Maudie is both Atticus's friend and supporter, and Maudie is quick to defend Atticus after the trial. Scout feels comfortable sitting with her older friend on Maudie's front porch, and when Maudie's house burns down, Scout is puzzled at how Maudie almost gleefully accepts the news, promising to build a smaller house so she will have more room for another garden. Scout seems to understand that Maudie (a widow) needs no man to lean on, and her quirky and independent nature blends perfectly with her love of the outdoors. The children have "considerable faith" in Miss Maudie, who
... after her five o'clock bath... would appear on the porch and reign over the street in magisterial beauty. (Chapter 5)