The opening paragraphs, in addition to being exquisitly written, help to establish for the reader two main things: Nick's narrative style and an aura of mystery about Gatsby. We can learn from Nick's "voice" that he is an educated person with a solid family background. His sophisticated vocabulary and his manner of speech clearly indicate a person of good breeding. The lengthy description of his family history gives him a sense of history and authority. If you read this section carefully, you will notice that Nick's family history parallels the development of America. They came over from Europe, established themselves in the East and than migrated to the Midwest. The fact that he uses the word "snobbishly" twice is also a clue to where his family sees itself. The point is that we, as readers, clearly understand Nick's background. We do not, however, have much to go on when it comes to Gatsby.
The second major point of these initial paragraphs is what we learn about Gatsby. We understand, first and foremost, that Nick is conflicted about his own judgment of Gatsby (and someone who says he "reserves judgment" at that). Gatsby is someone who represents "everything for which [he has] an unaffected scorn," yet "there was something gorgeous about him." We also learn that Nick admires Gatsby's "gift for hope" and "romantic readiness," and that he "turned out all right in the end." I urge my students not to forget these main characteristics of Gatsby, because it is this, plus what Nick says about him in Chapter 8 ("They're a rotten crowd. You're worth the whole damn bunch put together) that make Gatsby great.
Armed with this knowledge, readers can begin to see how Nick will become our guide through the sordid events of summer 1922 in New York, and Jay Gatsby will be our misguided romantic hero.