This chapter is the first one to introduce Gatsby himself. We as readers have met him indirectly so far, as we heard a lot of rumors and saw the narrator talking about parties and mysterious neighbor he never met personally.
Now, we meet Gatsby in person. He looks young and a bit distant. His smile is charming; his life is still a mystery. His habit of calling everyone ‘old sport’ seems falsely and strange. Still, we see, that the narrator is charmed by the character and the outlook of his new acquaintance.
Also, this chapter shows ‘the spirit of America,’ as we see all classes and social strata blending in a huge party. Everybody is invited and welcomed, people make connections and have fun all together. Still, the point of those parties is not clear so far.
Another focus of the story is clearly shown in the episode with the bookshelves. By this time the reader could fall for the opinion, that Jay Gatsby is a made-up person, whose whole life is a theater. We start imagining him to be cheating and lying in everything he does. So, it would be quite expected for him to have a fake library, with no books, but covers only. Still, the reader gets amazed by the fact that the library is real, just like the Owl Eyes man.