In this chapter, we learn that Atticus has real reservations about defending Tom Robinson and doesn’t think he can win, but he is willing to try.
In the conversation that Scout overhears between Jack and Atticus, we get a new perspective on Atticus. He is admitting that he is worried. He shares his strategy, which is to get people to think.
"Before I'm through, I intend to jar the jury a bit- I think we'll have a reasonable chance on appeal, though. I really can't tell at this stage, Jack. (ch 9)
Atticus does not believe he will win. He wants Scout to know this, but does not tell her outright. This makes the reader realize that Atticus is not the saintly paragon of wisdom that his children sometimes hold him up to be. He is up against an impossible task, and while he is virtuous enough to try to make a difference, he is not naïve enough to think he can win.
You know, I'd hoped to get through life without a case of this kind, but John Taylor pointed at me and said, 'You're It.'" (ch 9)
Lee includes this scene with Jack and Atticus as a way of demonstrating how lonely Atticus is. It is him against the town, and he is basically doing this all on his own. He is a target of ridicule, derision and harassment of all kinds. Yet even though Judge Taylor appointed him, he is going to try his best. As Scout will later learn, Atticus really is courageous.