How do the last four paragraphs, beginning with "most of the big shore places were closed now," effectively illustrate the themes of The Great Gatsby?
In these last four paragraphs, the past and the future merge as both become a source of ideas and dreams. These dreams are corrupted by materialism, making the corrupted or failed American Dream a theme of the novel.
On his last night before returning to Minnesota, Nick revisits the "huge, incoherent failure of a house" that has been Gatsby's. This mansion, imitative of a hôtel de ville, represents the failure of his American dream and the illusory path of Gatsby's life.
Gatsby's is one of the "inessential houses" that has begun to "melt away" in Nick's vision until he imagines the old island that Dutch sailors once discovered. It was a land of great opportunity, one vast and awe-inspiring. Indeed, this dream of the new continent must have been something like Gatsby's dream. Like the immigrants to America who believed in the new land of opportunity where one could reshape oneself and attain success and wealth, Gatsby too believed in limitless opportunity. Often he stood upon his illusory "blue lawn" before the imitation of a resplendent old-world structure, unaware of the "dark fields" of corruption that lay "under the night."
Thus, the once-pristine and real American Dream has become tawdry and venal as it has been corrupted by the immorality, deception, and ill-gotten gains generated from materialism. Only Gatsby continued to believe in the dreams and strive toward the green light at the end of the dock.
Here, Nick prepares to return home. He takes one last look at Gatsby’s house and remembers Dutch sailors arriving in the New World. He connects the “green breast of the new world” with Gatsby and concludes that like those first European arrivals to America, seeing Daisy's dock put Gatsby “face to face for the last time in history with something commensurate to his capacity for wonder.” For both the sailors and Gatsby, that was the last “transitory enchanted moment” when man “must have held his breath in the presence of this continent, compelled into an aesthetic contemplation he neither understood nor desired.” So Fitzgerald describes the American Dream.
Gatsby’s dream was actually behind him “somewhere back in that vast obscurity beyond the city, where the dark fields of the republic rolled on under the night.” The national dream, like Gatsby’s in all its idealism, asked too much. Yet his spirit never succumbed. Gatsby’s green light is both his yesterday and his tomorrow. It symbolizes the dream of his boyhood and the hope of fulfillment in the future. It represents the reckless, "success at any cost", pursuit of the entire American Dream. As Daisy blossoms for Gatsby, the new world had flowered for the Dutch settlers. Nick declares of the Dream, “It eluded us then, but that’s no matter—tomorrow we will run faster, stretch out our arms farther.… And one fine morning.…”.