On Chapter 20 of the novel To Kill a Mockingbird by Harper Lee we find Atticus giving his closing arguments to the jury in order to avoid an unfair verdict in the trial of his client, Tom Robinson.
Atticus Finch, from the beginning and after analyzing the evidence presented in this case, plus the lack thereof, realized that this was a case of an unjust nature. He (as he explained to the jury) knew that Mayella Ewell had done the "unmentionable" bad choice of kissing a black man, but that it was not Tom Robinson who beat and abuse her, but her own father, Mr. Ewell. In this assumption Atticus was more than correct. Mr. Ewell is an abuser of his children and Mayella used Tom as her excuse for wanting to kiss him and become intimate with him because she was a lecherous kind of person.
However, Atticus explains, that it is a normal thing for humans to try to judge. It is an easy thing to do: Just to assume that all people from a specific background are supposed to be and act in a certain way. Yet, Atticus explains that every human being has the same capacity for good and evil as the person next door. Everyone has the capacity for lust, for violence, and for many other things- therefore, it would be quite insolent from the part of the jury to convict Tom Robinson without looking at the evidence just for the sake that he is black, and that blacks are all criminalized.
In the end, Atticus closed with the words "for God's sake, believe him", which is a last plea to their consciences and to make them think outside the box. The people from Macomb were blindsided and narrow-minded. They would have not even bothered going through trial because they live on the assumption that all whites are good and all blacks are miserable. Atticus was begging and appealing to their common sense, which in Macomb is not a common denominator. As expected, Atticus lost his case, but he did not lose his credibility in Tom Robinson.