WOW! Good question!
The character of Attius Finch in Harper Lee's To Kill a Mockingbird is meant to represent an agent of social change who challenges the outwardly- content and calm nature of the town of Maycomb by, unwillingly, exposing their social inequalities for what they are.
This is significant because Atticus is a man who gives no indication that he would be the one person who would shake the very foundation of the town o Maycomb by accepting the unthinkable: To the defend in a court of law a black man accused of raping a white woman.
Scout tells us in Chapter 1 that Atticus is just another child of Maycomb, and someone very unlikely to stir any kind of issue in his small town.
He liked Maycomb, he was Maycomb County born and bred; he knew his people, they knew him.
However, when Atticus takes the case, the first reaction that is most noticeable is related by Scout when she says how children begin to mock her, and her family, since Atticus's defense of Tom Robinson becomes the prime talk of the town.
Atticus is nevertheless relentless and stands by his responsibility, ensuring that his children know that there is no difference in defending a black or a white person so long as the person is innocent and receives a due process.
This alone causes more revolt: The entire town wants to weigh its own traditional system of believe against that of just one man who seems to be stronger, and who is obviously much more courageous than all of the other men, combined.
Yet, Atticus is at all times between a rock and a hard place. In his aim to do what is right, he is willing to open up and see things for what they really are: Maycomb may not like what he is doing, but he will not give up to please his people: He will move forward and change the face of justice in Macomb. His versatility, his intelligence, and his poise during the trial earns him a respect that no other person had acquired, and, with that respect, comes anger and resentment. It is for this reason that men come to try and lynch Tom Robinson, they try to directly fight with Atticus Finch, and they do their best to humilliate his actions towards Robinson in aims to bring him down.
The influence of Atticus over Maycomb is not intentional nor planned: Maycomb simply undergoes the effects of a changing world that, at some point has to touch a very backwards town and it is through Atticus that this change finally comes to happen.