By the time we get to chapter 23 in To Kill a Mockingbird, we know that Tom Robinson has been found guilty, although Atticus has proved that there was no way Tom could have committed the crime. Bob Ewell is still terrorizing Atticus and anyone he thinks wanted Tom to be set free. Jem knows that Tom's appeal is coming up and wonders why the jury didn't decide the penalty for Tom.
"Given," said Atticus. "Tom Robinson's a colored man, Jem. No jury in this part of the world's going to say, 'We think you're guilty, but not very,' on a charge like that. It was either a straight acquittal or nothing."
Atticus knows that the chances that Tom will be acquitted are slim, but he is trying to explain to Jem that because Tom is black, the jury had already made up their mind. It didn't matter what the crime was, or that Atticus had proved that he was innocent; Tom was black, and that was all the jury needed to know. Atticus is telling Jem that in the part of the country they live in, the south, the people are very narrow-minded and judge someone just on the color of their skin. If you turn on the news today, you will see that we still have a long way to go.