A chief way that Fitzgerald's use of figurative language enhances the novel is by projecting a sympathetic and romantic portrait of Gatsby. The soul-killing Tom's hard-headed appraisal that Gatsby is a low-life criminal is not wrong, but, as Nick shows, it does not capture the essence of who Gatsby is and what makes him "great." For that, we need Nick's lyrical language.
Nick's figurative language surrounds Gatsby with a soft glow. Whether he is describing the preparations for one of Gatsby's great parties or the tragic grandeur of Gatsby's dream of reconnecting with Daisy and starting over, Nick conveys his admiration of Gatsby's willingness to dream and live expansively.
Some of the most famous quotes in this novel express the poetry of Gatsby's life. In this one, Nick likens Gatsby to the American dream itself, the capacity for wonder:
Gradually I became aware of the old island here that flowered once for Dutch sailors’ eyes—a fresh, green breast of the new world . . . For a transitory enchanted moment man must have held his breath in the presence of this continent, compelled into an aesthetic contemplation he neither understood nor desired, face to face for the last time in history with something commensurate to his capacity for wonder.
Nick's use of imagery (the "fresh, green breast"), and the series of alliterative "c" sounds that create a sense of rhythm, raises Gatsby's story to poetry. Nick contrasts Gatsby's romantic readiness and willingness to dream big with the "foul dust" he encounters in the form of people like Tom Buchanan.