Nick Carraway, the novel's narrator, is a young man who was born into a conservative, well established, but not wealthy, Midwestern family. After attending college and serving in World War I, Nick comes back home, but he finds the Midwest seems out of the mainstream of life as he has come to know it out in the world. With his family's financial backing for one year, Nick goes to New York to learn the bond business and establish a career in the East. Nick's work ethic is strong; he works hard, but he also becomes involved in the lives of his mysterious neighbor, Jay Gatsby, and his distant cousin Daisy Buchanan and her husband Tom (whom Nick had known in college).
In addition to functioning in the novel as the narrator who observes and reports, Nick plays another important role. Through Nick, Fitzgerald establishes and develops a sharp contrast between the East and the Midwest. It is through this contrast that the novel's major theme is developed: the corruption of the American Dream in modern society. Nick becomes Fitzgerald's voice of moral authority.
When Nick moves to the East, he is a young man with an open mind and a non-judgmental nature. He is also a young man who was shaped by his family's Midwestern values. Nick leaves the Midwest never intending to return; however, even though his family had financed him for a year, Nick leaves New York to go back home after only a few months. Once he is back home, after many months he is still dealing with all that he experienced and observed in the East, and he is no longer a man who reserves judgment.
Nick makes strong moral judgments as a result of his time in New York. Primarily, he rejects the amorality and corruption of the Buchanans. The last time he sees Tom, after Gatsby's death, Nick does not want even to shake his hand; he does shake Tom's hand because he knows that Tom is so morally bankrupt he wouldn't even understand the gesture. Nick is a decent person; he is sickened by the "foul dust that floated in the wake of [Gatsby's] dreams."
Fitzgerald began the novel with a discussion of the Midwest, and in the novel's final chapter, he included a beautiful passage in which Nick talks about "my middle-west," a place where dwellings are still called through decades by a family's name." By turning his back on the East and going home, Nick makes Fitzgerald's moral statement.