The words at the very beginning of the story become a sort of a marker, they are a hint of how we should interpret the whole novel. Mainly they stress the difference between people inhabiting the two describe neighborhoods, West and East Egg. They seem to be similar at the first sight, like, both are rich, have a lot of money and opportunities, both like to show off with their wealth, but there is a deep and significant difference between them. Namely, it is all about the parentage and gained an education. This is the main line drawn between the two districts, and this is the main thing that explains the hostile relationships those two groups of people share.
Nick plays the role of a link between West Egg and East Egg districts. He clearly belongs to the East Egg due to the noble parentage and great education, but he is a bit short on money, so he is convinced to stay on the other side, even though he differs from his neighbors.
We also see how other characters display the general mood and behavior of each district. Jordan, for example, is a typical inhabitant of the East Egg. She is bored, cynical and seems to have no interest in everything that surrounds her. The same can be told about Tom, he is arrogant, deceitful and seems to be not very concerned about his reputation, as his affair is not that ‘secret’ as it has to be.
On the other hand, we see Gatsby, who is described as a typical inhabitant of the West Egg. He is rich and shows off on any occasion. He throws huge parties, has only the best, the newest and the most expensive stuff and, most important, he keeps his true life story secret. His motives, values, the origin of his wealth are all classified. Everybody gets a false made-up story on anything in his life.