In To Kill a Mockingbird, at whom is Atticus's final address to the jury aimed?

In many ways, Atticus' final speech is directed at the town as a whole, really at anyone who still harbors the desire to see certain people as less equal than others. He makes a very broad appeal by noting that there isn't a single person in the courtroom who hasn't done what Mayella Ewell has done, that there isn't anyone who hasn't done something immoral or looked upon another person with lust or lied. Atticus knows that he isn't just trying to convince the whole jury but that he is working against the prejudice and prejudicial history of an entire town in trying to help them acquit Tom Robinson of a crime the trial demonstrated that he did not commit.

This appeal is based on the hope that by connecting with these weaknesses that all humans have he can stir in them a desire to do their duty as humans rather than as citizens of a town that is liable to make decisions based on prejudice and ignorance instead of logic. In the end, when he asks them to "do their duty," Atticus is asking them to go against the culture of the town and their lives up to that point and to do the honest thing for Tom and for themselves as a society.