How does Atticus help the townspeople in Harper Lee's To Kill a Mockingbird?

Atticus helps the townspeople by being their advocate for law and morality in Harper Lee's To Kill a Mockingbird.

One way in which Atticus serves as an advocate for both law and morality is through his decision to defend Tom Robinson. As Atticus explains to his brother in Chapter 9, he had hoped to progress through his career without having to deal with a case that is doomed to failure due to racial prejudices, yet when Judge Taylor assigned him to the case, Atticus knew he was morally obligated to take it because he knows all charged with a crime are entitled to the best defense possible and to be considered innocent until proven guilty. He also knows he is morally obligated because no concrete evidence exists to legitimately convict Robinson. As Atticus explains to his brother, "The only thing we've got is a black man's word against the Ewells'. The evidence boils down to you-did--I-didn't" (Ch. 9). More importantly, Atticus is defending Robinson despite objections raised by the townspeople. All throughout the novel, we see that many racist townspeople assume that Robinson is guilty because they hold a prejudiced belief that all African Americans behave immorally. Hence, Atticus is acting as the voice of legal and moral reason by upholding his principles and putting his all into defending Robinson.

While Atticus's defense of Robinson does not have a significant impact on the townspeople, as evidenced by the fact that Robinson is still found guilty despite all evidence to the contrary, Robinson's defense does have a tiny impact. In Miss Maudie's opinion, the fact that the jury was out so long with its decision testifies to the small impact Atticus's defense of Robinson made. In Miss Maudie's view, the town is "making a step--it's just a baby-step, but it's a step"--towards creating a more just society; Atticus's role as Robinson's defense attorney has helped move the town to make its baby step (Ch. 22).

Despite the fact that many of the townspeople objected to Atticus's decision to truly defend Robinson, the townspeople's decision to re-elect Atticus unchallenged to the state legislature shows that Atticus has still had an impact on the townspeople by influencing both their sense of morality and their sense of justice. Scout notes in the following the peculiarity of the townspeople's re-election of Atticus, despite their protestations that Atticus is a poor father who behaved disgracefully by putting his all into defending Robinson:

There was one odd thing, though, that I never understood: in spite of Atticus's shortcomings as a parent, people were content to re-elect him to the state legislature that year, as usual, without opposition. (Ch. 26)

However, Scout is too young to see that the townspeople's decision to re-elect Atticus shows they genuinely respect him as Maycomb's most upright citizen; they are just too prideful to admit it. Hence, though Atticus has not yet helped the townspeople to rid themselves of their prejudice, he has at least impacted their views of morality and justice in a tiny way.