Nick is the morality of the novel. He has been raised in the Midwest with ethical and moral values. His father has given Nick moral stability and advised him not to judge anyone since not everyone has had the opportunities he has had. Nick is also a realist, and the other characters are not. Nick sees things as they really are, and although he is pulled into Daisy's and Jordan's sordid world at first, he realizes that they live meaningless lives and are incapable of caring about anyone or anything besides themselves. Nick is the only character who recognizes the goodness and sincerity of Gatsby, and this is why Nick tells Gatsby that Gatsby is better than the "whole rotten bunch put together".
Nick serves as a representative of every man who could peek into the world of the 1920s. Nick's not really rich, or overly popular or completely successful as a businessman. He is middle class and from a working class family in the Midwest. This is a majority of America.
The lens through which he looks helps us see characters for who they are and with appropriate and necessary judgment. Although as a narrator Nick claims he doesn't really judge people, his words are dripping with adjectives and adverbs that place value on other characters actions.
His relationship with Jordan shows a natural effort at a relationship and the bumps of a not necessarily successful dating relationship. He is a good all-American boy.
The first thing that stands out is that he is not initially engaged in the sinful lifestyles of the other main characters in the work. Gatsby, Tom, Myrtle, and Daisy are all associated with adultery. Gatsby is engaged in illegal money-making ventures. Tom is arrogant and abusive. Nick, although by no means a perfect character, avoids the despicable behavior most of his peers engage in. Also, Nick is not directly responsible for any of the major wrongdoings that lead up to the climax of the novel.
Nick is also different because he has not rich like most of the other main characters.