In To Kill a Mockingbird, what fact about Atticus's defense of Tom Robinson does Scout learn from the Idlers' Club?

In Harper Lee's To Kill a
Mockingbird, in Chapter 16, Jem, Dill and Scout make their way into the
courthouse as the trial of Tom Robinson is about to
begin.

Scout becomes separated from the boys and finds
herself in the midst of the Idlers' Club, a group of men who know the court system very
well, according to Atticus, because they spend so much time at the
courthouse.

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This was a group of white-shirted,
khaki-trousered, suspendered old men who hd spent their lives doing nothing and passed
their twilight days doing same on pine benches under the live oaks on the
square…Normally, they were the court's only spectators, and today them seemed resentful
of the interruption of their comfortable
routine.

The courthouse is
packed and the Idlers' Club does not have the place to themselves as is usually the
case. While Scout tries to stand unnoticed, she listens to the men speaking, realizing
that Atticus is the topic of their conversation—Scout learns here that Atticus was
appointed to defend Tom Robinson, which puts a new light on
things.

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"Lemme tell you something' now, Billy," a third
said, "you know the court appointed [Atticus] to defend this
n***er."

"Yeah, but Atticus aims to defend him. That's what
I don't like about it."

Scout
figures that this news may change the way everyone acts regarding Atticus' defense of
Tom Robinson—the alleged (black) rapist of a white
woman.

This
was news, news that put a different light on things: Atticus had to, whether he wanted
to or not. I thought it odd that he hadn't said anything to us about it—we could have
used it many times in defending him and ourselves. He had to, that's why he was doing
it…But did it explain the town's attitude? The court appointed Atticus to defend him.
Atticus aimed to defend him. That's what they didn't like about it. It was
confusing.

Scout realizes
that her father was assigned the case. He is a lawyer and plans to do his best by Tom
Robinson. She notes that the situation is a confusing one to her: this is because the
prejudiced members of Maycomb's population would understand the
court case being assigned to him, but would
NOT understand his decision to do his duty as a servant of the
court and the people he defends—if that defendant is black. The man is inferring that he
wishes Atticus chose to do nothing for Tom. However, we know
Atticus too well: he judges people for their character (and even then, quietly), rather
than by their skin color. He is a man of principle who would never turn someone down if
he or she asked for his help.

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Atticus represents the moral backbone of the town
of Maycomb, deep in the South.