Why does Atticus undress in the court room?

In Chapter 20, Scout and Jem notice their father do something that they have never witnessed him do before. Atticus casually unbuttons his vest, the collar of his shirt, loosens his tie, and takes off his coat. They are shocked and confused as to why Atticus is undressing in front of the jury. As Atticus begins to give his closing remarks, Scout mentions, "His voice had lost its aridity, its detachment, and he was talking to the jury as if they were folks on the post office corner" (Lee 124). Atticus then proceeds to encourage the jury to judge the Tom Robinson case without their prejudiced beliefs. The reason Atticus begins to "undress" is because he wants to portray himself as a typical citizen of Maycomb. He is attempting to connect with the jury on a personal level, which is why he strips himself of his formal attire to appeal favorably to the jury. He begins to talk to the jury like they were "folks on the post office corner" to make them feel comfortable and familiar. Atticus is trying to give the impression that he relates to the jury's difficult situation; he hopes that they will look past their prejudice and accept Tom's testimony as the truth.