Most important event in chapter 3 of Great Gatsby?

In this chapter, Jay Gatsby remains fundamentally a mystery. Few of the partygoers have met their host, and Gatsby stands aloof from his own celebration. He does not drink, he does not dance, he remains an observer. The man himself stands in stark contrast to the sinister gossip Nick has heard about him. Gatsby is young and handsome, with a beautiful smile that seems to radiate hope and optimism. Nick falls instantly in love with Gatsby's smile, remarking that it has "a quality of eternal reassurance in it." Gatsby's innate hopefulness is contagious.