why do you think the description of the ash at the beginning of Chapter 2 is important? 

The road from West Egg to New York City exemplifies decay. It is a "valley of ashes," a place of uninterrupted desolation. The eyes of Doctor T.J. Eckleburg are an indelibly grotesque image: these are eyes unattached to any face or body, gazing out over a hellish wasteland. Fitzgerald's description of the drawbridge and passing barges makes an allusion to the River Styx, a mythological river which one crosses to enter the realm of the dead. The eyes of Dr. T.J. Eckleburg seem to be a monstrous parody of the eyes of God: they watch, but they do not see; they are heartless, and entirely unknowing. Like the scene in which Gatsby reaches for the green light, high symbolism is given priority over the demands of realism: the reader is presented with an implausible, but highly effective image of two detached eyes looking out over dust and ashes.