At the end of chapter one, the courtroom has been waiting on the jury to deliver its verdict on the Tom Robinson case. They waited for quite some time, and finally heard the verdict of guilty. It was a devastating blow to Jem and many others in the courtroom, who had so much hope, considering the irrefutable evidence in Tom's favor. After all of that work, after all of the evidence given, Tom was still found guilty, which shows just how powerful a grip racism had on the hearts of many of the jury members.
However, the guilty verdict is not the most significant aspect of the end of that chapter. A guilty verdict was anticipated by almost everyone, everyone who knew Maycomb well, that is. What is even more significant is that as Atticus stands up to leave and is walking down the aisle to the exit,
"all around us and in the balcony on the opposite wall, the Negroes were getting on their feet."
The black community, in an act of respect to Atticus and all that he did to defend Tom stood in a show of support and reverence as he passed by. When people stand as someone passes, it is usually someone important; think of the president of the United States--when he enters a room, as a show of respect for his position, everyone stands. The black people in the courtroom that day wanted to show Atticus how much they appreciated the very difficult case that he took, and for the honest, hard-working job that he did. They respect him very greatly, and showed it through their solidarity in rising as he passed through. That is significant; it shows, in a small way, what a great man Atticus was. It also shows that the black community did not hold Tom's guilty verdict against Atticus--they knew it wasn't his fault, but the fault of the racist beliefs of the town. They knew he did his best, and gave an honest trial. I hope that helped; good luck.