Fitzgerald tells the entire story of The Great Gatsby from the viewpoint of Nick Carraway. While Nick's perceptions and comments give us insight and understanding of the other characters in the story, they also provide information about the general society of that era.
Nick and the others were members of the "lost generation" - the group that reached young adulthood in the immediate aftermath of World War I. This group was very concerned with making money and securing financial gain for themselves. They were anxious to enjoy the good life, as symbolized by wild parties and generous consumption of alcohol and other forbidden substances, especially after Prohibition came into effect. The women were interested in maintaining and expanding individual rights they gained during the War - this was the age of the suffragettes leading to women being given the right to vote.
Nick's voice tells us of the loneliness, longing and disillusion of the lost generation, the group of young adults who were scarred by the carnage and seemingly meaningless waste of lives in World War I.
The loneliness of the main characters permeates the book. Gatsby, filled with desire to reconnect with Daisy, has no real friends and lives in isolated splendor in his mansion, standing apart even when his house is filled with guests. Daisy lives in lonely misery while Tom cheats on her. Tom tries to fill his own void with a series of affairs with lower class women. Nick wanders the streets of New York alone at night, longing for the company he sees behind lit windows. He and Jordan, an enigmatic figure, cling to each other out of mutual need but never truly connect.
Nick's lyrical writing voice underscores his longing for what he believes is the lost American Dream, a dream he thinks was always just that. But he primarily, at least for a time, experiences disillusion: a disillusion that crystallizes itself around what happened to Gatsby: "it is what preyed on Gatsby, what foul dust that floated in the wake of his dreams, that temporarily closed out my interest in the abortive sorrows and short-winded elations of man."
These characters are part of a generation that drowns out its cynicism in drinking, wild parties and material excess--while Nick himself finally retreats into his Midwest past of "street lamps and sleigh bells in the frosty dark ... I am part of that." But he also carries with him the more recent, less idyllic past he can't erase.