In the final passage of the novel, Nick uses poetic language to relate an idea of Gatsby while also presenting a reiteration/encapsulation of some of the novel's themes.
The land (New York) is described as being a place open to the creative impulse, open to being shaped and stretching also far and wide, implying a vastness that is also commensurate with man's ability to dream.
For Gatsby, this same part of the earth took on a very similar appeal. Gatsby's dream of finding and marrying Daisy is set here, on the same place - New York.
In this comparison, Nick presents a conception of the American Dream and aligns Gatsby with this dream, even in all his fantastic, ostentatious and impossible visions of success. His dream is paralleled here with the dream of the Dutch settlers, a symbol of an original version of the proverbial American Dream - of success and of self-determination.
For Gatsby, the only recognizable limits to achievement were the limits of his dreams. This idea and Gatsby's idealism are encapsulated in this coda as Nick closes out his story.