Arguably the most important element of the plot in Chapter 1 is Nick's introduction to the social world, in which he will move throughout the rest of the story. After arriving on the East coast, Nick quickly notices the difference between West Egg—inhabited by nouveau riche arrivistes such as Gatsby—and East Egg, where the old money elite live. This tension between old money and new is an important one that will develop throughout the story, most notably in the faltering relationship between Gatsby and Daisy Buchanan.
As we're introduced to an unfamiliar world of wealth and glamor, it's vital that we have someone who can make sense of it all, with whom we can feel some kind of connection. And that's the role of Nick Carraway. His Midwest background and common sense allow him to provide a commentary on the faintly ridiculous world in which he's now arrived. Like most readers, Nick is fascinated and repelled in equal measure by the East and West Eggers and the lives of opulent boredom they lead. In Chapter 1, he provides us with a way into their little world, but without going too far. We're being eased ever so gently into their natural environment, the better to prepare us for what will happen later.