Mr. Raymond,who is looked down upon because he has fathered children of mixed race, tells Dill and Scout that he is not really a drunk as the townspeople believe. He has chosen to act the part, weaving a little and drinking out of a paper sack, in order to give people a reason they "can latch onto" for disapproving of the way he lives.
Mr. Raymond knows that the town condemns him because he has defied a social standard rooted in prejudice. People cannot admit that the reason for their condemnation is rooted in bigotry, however. It is easier for them to blame his chosen lifestyle, and their disapproval of it, on his drunkenness, and so, even though he sips only Coca Cola from his sack, Mr. Raymond obligingly allows them to cling to this misconception. Mr. Raymond also says that he is telling his secret to Scout and Dill because, as children, "things haven't caught up to (their) instinct(s) yet." Because of their innocence, they see the truth as it really is, uncolored by social expectations (Chapter 20).
Mr. Raymond's revelation is important in this chapter because, as the scene shifts to the courtroom where Atticus is defending Tom Robinson, it is evident that the only reason Tom might be declared guilty is because of social preconceptions rooted in racial intolerance. In order to convict Tom, the jury must deny the truth and rationalize away the evidence of their own biases by hiding behind long-standing social beliefs.