In Chapter 9, Scout tells her father what Cecil Jacobs said on the playground about him defending niggers, and Atticus elaborates on his unpopular decision to defend Tom Robinson. When Scout asks her father why he chooses to defend a man against the community's wishes, Atticus tells his daughter,

"For a number of reasons...The main one is, if I didn’t I couldn’t hold up my head in town, I couldn’t represent this county in the legislature, I couldn’t even tell you or Jem not to do something again" (Lee, 49).

Atticus knows that Tom Robinson is innocent, and not defending him against a prejudiced community would be immoral. Being that Atticus is a morally upright man with integrity, he feels obligated to do the right thing, which is to defend Tom Robinson despite the community's beliefs. If Atticus chose not to defend Tom Robinson, he would be going against everything he believes in. Atticus feels like his words would have no authority because he would lose his integrity if he followed the popular decision of not defending Tom Robinson. Atticus cannot go against his conscience and feels obligated to do the right thing, which is why he courageously defends Tom Robinson in front of a prejudiced community.

First, this quote defines Atticus's character.  When he says that he could not hold his head up in town if he didn't defend Tom, he means that he has spent his life trying to do what is right and moral.  He knows, and he truly believes that his town knows, that the right thing to do is to defend and protect Tom from a racist, false accusation.

The second part of his quote--"I couldn't represent this county in the legislature"--establishes that Atticus does not simply try to live a personally moral life.  He wants his county to exemplify a group of people who are just and forward-thinking.  Because of his strong moral attributes, it would go against Atticus's ideology to know that his county really cares nothing about justice and to have to represent them with passion and loyalty to others.  Atticus sees Tom's case as a bellringer of how his county and small town will be remembered, and he wants no part in going down in history as one who contributed to prejudice and simple-mindedness.

Finally, Atticus is such an ideal father because he strives to teach by example.  All of the morals and lessons he imparts to his children are ones that he truly believes.  He doesn't simply tell them to live those morals because they will be better people; he lives those morals himself because he believes them himself and hopes to make the world a more just place.

Atticus tells Scout this so that she will realize that his choice to defend Tom Robinson is a moral choice.

Atticus says that there is a case in every lawyer’s career that “affects him personally” (ch 9, p. 100). His point is that he takes the case seriously because it requires him to make a moral decision. He has to stand up not just for Tom Robinson, but against the town. He has to make the choice to do what he thinks is right.

“Simply because we were licked a hundred years before we started is no reason for us not to try to win,” Atticus said. (ch 9, p. 101)

Atticus is telling Scout this so that she will learn a life lesson. It is a person’s responsibility to stand up for what he or she believes in. You need to stand by your choice, if you think it is right, even if it is not the most popular choice. This is the strongest lesson that Atticus teaches Scout. He leads by example, showing her that it is important for a person to do the right thing. This is the only way that racism can be overcome.

It is also significant because "Atticus represents the moral backbone of the town of Maycomb" (enotes, character analysis). By standing up for what he feels is right, he is showing the town what is right. Ultimately this does make a difference, because the jury does at least consider Tom Robinson's potential innocence.

To read more character analysis, see here: http://www.enotes.com/to-kill-a-mockingbird/character-analysis

To read a summary of this chapter, see here: http://www.enotes.com/to-kill-a-mockingbird/chapter-9-summary-analysis

Citation:

• Enotes. "To Kill a Mockingbird: Character Analysis." Enotes.com. Enotes.com. Web. 17 May 2012. <http://www.enotes.com/to-kill-a-mockingbird/character-analysis>.
• Lee, Harper. To Kill a Mockingbird. New York: Warner, 1986. Print.