Answer:
Build dramatic tension
Step-by-step explanation:
Although the reader is fully aware of how difficult it would be for Atticus to win the trial, Jem's confidence is meant to inspire us to have a little hope. Jem truly believes that justice is going to win, and his confidence serves to make the reader more unsure. This contributes to building dramatic tension, as it makes the reader more eager to know the eventual outcome and to hope for a positive one.