It was the first day of second grade and Billy Miller was worried. He was worried that he wouldn’t be smart enough for school this year.
-- Narrator (Part 1, Chapter 1 paragraph 1)

Importance: The narrator explains that this is the first day of Billy Miller's second grade year at school, and reveals right away that Billy is worried because he doesn't think he will be smart enough. This stems from a fall from a lookout platform Billy endured while on summer vacation, in which he hit his head pretty hard, but not hard enough to cause any real damage. It is the first concern of many that Billy will have over the course of the novel.

Mrs. Silver and the great nation of China might think that this is the Year of the Rabbit,” said Papa. “But I know –and I know everything –that this is the year of Billy Miller.
-- Papa (Part 1, Chapter 1 paragraph 37)

Importance: Papa reassures Billy that, yes...