What effect does the structure of The Great Gatsby have on the book as a whole?

Nick arrives from the Midwest and returns to it at the end, so the story is a complete, realized whole. That completeness gives a finality and authority to his final connections on American history in Chapter IX. The novel also builds to a conclusion in chapter VII, when Gatsby's dream of recapturing Daisy is shattered and he is (as a result of the accident) killed. The denouement is thus protracted, and the drawn-out feature underscores the brooding, meditative quality of the conclusion.