Author Harper Lee uses Atticus's Christmas conversation with his brother Jack to foreshadow later events in Part Two of the novel. Scout has already gotten into a fight with her cousin Francis after he has called Atticus and Scout "nigger-lovers," and Atticus knows that things will only get worse as the trial nears. Although Scout seems to respond positively to most of her one-on-one discussions with her father, Atticus must have decided that allowing her to think she is overhearing some serious talk with Jack will let her believe that she is privy to some important secrets. But when Atticus suddenly stops and calls out her name, "My scalp jumped." She "scurried to my room" when he demanded that she "Go to bed," and it made Scout even more in awe of her father's apparent omniscience.
I never figured out how Atticus knew I was listening. (Chapter 9)
It was only "many years later that I realized he wanted me to hear every word he said." Lee also wants the reader to know just how serious the trial will be to the town of Maycomb, how "reasonable people go stark raving mad when anything involving a Negro comes up," and how it will be important that "Jem and Scout come to me for their answers" and that "I hope they trust me enough." Much of Part One has consisted of humorous exploits by the children to get a glimpse of Boo Radley, but Lee is letting the reader know that such will not be the case once the trial gets underway.