The overall message, or theme, in To Kill a Mockingbird is that every human being deserves to be treated with dignity.
In the beginning of the story, we learn that children should be treated with dignity. Scout is offended when her new teacher Miss Caroline punishes her instead of listening to her, and complains that her father taught her wrong.
Scout also advises her Uncle Jack on how to respect children when he spanks her for cussing.
"Well, in the first place you never stopped to gimme a chance to tell you my side of it- you just lit right into me. When Jem an' I fuss Atticus doesn't ever just listen to Jem's side of it, he hears mine too…” (ch 9)
Poor Scout is learning that the world isn’t fair, but she has a point. Everyone, even a child, deserves to be listened to before a judgment is made.
We also learn that you should respect people regardless of how different they are in To Kill a Mockingbird. Boo Radley is the ridicule of the neighborhood because he had some trouble in his younger days and has been locked up in his house ever since. Children make fun of him and adults gossip about him, but in the end we learn that he is a kind, sweet, gentle man who never wants to hurt anyone and just wants to be left alone.
Atticus was right. One time he said you never really know a man until you stand in his shoes and walk around in them. Just standing on the Radley porch was enough. (ch 31)
He befriends Scout and Jem, looking out for them and giving them gifts. He also saves their lives.
People of all social classes deserve respect. Calpurnia and Atticus lecture Scout on her treatment of Walter Cunningham when she protests his use of syrup while visiting their house for lunch.
“Don't matter who they are, anybody sets foot in this house's yo' comp'ny..” (ch 3)
This is a lesson everyone needs to learn. You should always respect anyone, and not think you’re better than anyone, just because you are from a “better” family or have money.
Finally, we need to treat people as equals regardless of color. Atticus teaches his children this, by example. He is respectful of everyone. In the courtroom, he explains that most evidence was presented with confidence.
[They presented evidence] confident that you gentlemen would go along with them on the assumption- the evil assumption- that all Negroes lie, that all Negroes are basically immoral beings … (ch 20)
This is the moral of the story. Everyone is equal, regardless of the color of his or her skin. Skin color does not make one inferior—actions do.