Atticus is a voice of reason and morality in To Kill a Mockingbird. He is so honest and objectively ethical that he has an almost God-like status. He teaches with words and also by example. He gets Tom Robinson's case because no one else is up to the challenge. He does not respond to Mr. Ewell's violence against him, not because he is afraid, but because he is able to consider Mr. Ewell's perspective, concluding that if he is the brunt of Mr. Ewell's anger, this might save one of Mr. Ewell's children a beating.
This is the lesson running throughout the novel: to be able to see things from the perspective of others. When Mr. Ewell spits on Atticus, he just walks away, saying he's too old to fight. In Chapter 23, when Jem confronts Atticus on this, Atticus says, "So if spitting in my face and threatening me saved Mayella Ewell one extra beating, that’s something I’ll gladly take." Atticus is even willing to consider the perspective of ignorant racists like Mr. Ewell because of the implications his actions may have for Mr. Ewell's children.
It is because Atticus looks at things objectively that he not only stands against racism but he understands why people in Maycomb have (unfortunately) held on to their racist history.
Atticus stands for morality in the book. He is the epitome of a fair man who stands his ground. He raises his kid with dignity, poise, and purpose. This was Harper Lee's way of showing her perfect, ideal man and therefore society, even though this cannot exist (which is why the townspeople all counteract Atticus when he takes the court case). Most people say, including Harper lee's sister, that Atticus was modeled after the author's own father.