Jem firmly believes that his father is suggesting that the jury would be deciding in Tom Robinson's favor. He, Scout and Dill have been surreptitiously witnessing the court proceedings and Jem, especially, has been quite impressed by the manner in which his father came to Tom's defense. Atticus had essentially questioned the veracity of both Mayella Ewell and her father's testimony, creating doubt. So convinced was Jem that he, after Bob Ewell's cross examination by Atticus, reacted in the following manner:
Jem seemed to be having a quiet fit. He was pounding the balcony rail softly, and once he whispered, “We’ve got him.”
He believed that Atticus had caught Bob Ewell in a lie and had created reasonable proof that it was he who had beaten his daughter since he was left-handed and Mayella had sustained injuries to the right side of her face. Later, when he saw Tom Robinson's withered arm, he reacted as follows:
“Scout,” breathed Jem. “Scout, look! Reverend, he’s crippled!”
Jem had been engrossed in the proceedings and had even taken to explain the finer points of the trial to Dill. He regularly commented about what was transpiring and clearly assumed that everything would go his father's way. He had told Scout with great assurance:
“He’s just gone over the evidence,” Jem whispered, “and we’re gonna win, Scout. I don’t see how we can’t. He’s been at it ‘bout five minutes. He made it as plain and easy as—well, as I’da explained it to you. You could’ve understood it, even.”
Jem emphatically believed that Tom Robinson was going to be set free when he asked:
"You think they'll acquit him that fast?"
Jem's response to his father's remark about everything being over soon, put Atticus in a difficult position and all he could do was say nothing. Jem's belief illustrates his naivety and his innocence. He could not comprehend and had no real insight into the deep racial prejudices which were rooted into his community. He felt that evidence was enough to prove innocence or guilt and his idealistic notion of justice was shattered when the verdict finally came through, markedly explained in Scout's observation:
I peeked at Jem: his hands were white from gripping the balcony rail, and his shoulders jerked as if each “guilty” was a separate stab between them.
It is poignantly ironic that Atticus had said, in his summation:
“But there is one way in this country in which all men are created equal—there is one human institution that makes a pauper the equal of a Rockefeller, the stupid man the equal of an Einstein, and the ignorant man the equal of any college president. That institution, gentlemen, is a court. It can be the Supreme Court of the United States or the humblest J.P. court in the land, or this honorable court which you serve. Our courts have their faults, as does any human institution, but in this country our courts are the great levelers, and in our courts all men are created equal."
For Jem, justice such as this had not come to Maycomb.
At this point in the story, the trial is all but concluded. The jury is still out and the entire courtroom waits silently for a verdict. When Calpurnia enters and alerts Atticus to the fact that his children are missing, he realizes for the first time that they have been in the courtroom all along.
Atticus immediately sends the children home with the promise that if they eat, they can come back to hear the verdict. He is sure, however that "it'll be over," before they get back. To this, Jem replies, "You think they'll acquit him that fast?"
Jem, who has been following the entire trial very closely, is convinced that Atticus has proven Tom Robinson's innocence. He misinterprets his father's words because he is too young to understand the underlying issue of prejudice present. Despite the fact that he tried the case to the best of his ability, even Atticus knows the jury will not rule in Tom Robinson's favor. He assumes a quick verdict of "guilty." His son, hopeful, somewhat starstruck by his own dad, and yet untouched by any societal pressure toward bias and racism, feels confident that "we've won it."