What does the following quote from To Kill a Mockingbird mean? “People generally see what they look for, and hear what they listen for, and...

To understand why Judge Taylor says this, one would have to take it in context of the story. In chapter 17, Bob Ewell is giving his testimony about what happened on the day his daughter was allegedly raped. The whole county is in attendance: men, women, and children. Bob Ewell doesn't sugarcoat what he says even if there are innocent ears in the courtroom. When he gets to the part where he supposedly sees Tom raping Mayella, he says, "I seen that black ni**** yonder ruttin' on my Mayella!" (173). This causes quite a raucous in the audience and Scout says that Judge Taylor had to use his gavel for five minutes before anyone would listen to him. This is when Judge Taylor says the following:

“There has been a request . . . that this courtroom be cleared of spectators, or at least of women and children, a request that will be denied for the time being. People generally see what they look for, and hear what they listen for, and they have the right to subject their children to it, but I can assure you of one thing: you will receive what you see and hear in silence or you will leave this courtroom, but you won't leave it until the whole boiling of you come before me on contempt charges" (174). 

Judge Taylor permits women and children to stay because everyone is going to hear and see things differently anyway; so, there's no use banning anyone from the courtroom. He gives parents the discretion to decide if they want their children to be involved in the case that day and feels no need to control people's choices. However, if they do choose to stay, they stay at their own risk, they will be quiet, and they will not disrupt the proceedings. Otherwise, the consequences will be that he charges them with what is called contempt of court. That means they will get fined, and maybe even jailed, depending on a person's infraction or disruption of the case. Since everyone knows everyone else in Maycomb, the audience members should not have been surprised to hear such crass talk coming from Bob Ewell. Judge Taylor therefore refuses to babysit anyone who chose to listen in on this case.