The green light at the end of the east egg dock by Daisy's house symbolises Gatsby's hope to get back together with Daisy. It is the only reason that he moved to a house right opposite hers.
The valley of ashes represents the moral and social decay that results from the uninhibited pursuit of wealth, as the rich indulge themselves with regard for nothing but their own pleasure. The valley of ashes also symbolizes the plight of the poor, like George Wilson, who live among the dirty ashes and lose their vitality as a result.
The eyes of Doctor T. J. Eckleburg are a pair of fading, bespectacled eyes painted on an old advertising billboard over the valley of ashes. They may represent God staring down upon and judging American society as a moral wasteland, though the novel never makes this point explicitly. Instead, throughout the novel, Fitzgerald suggests that symbols only have meaning because characters instill them with meaning. The connection between the eyes of Doctor T. J. Eckleburg and God exists only in George Wilson’s grief-stricken mind. This lack of concrete significance contributes to the unsettling nature of the image. Thus, the eyes also come to represent the essential meaninglessness of the world and the arbitrariness of the mental process by which people invest objects with meaning. Nick explores these ideas in Chapter 8, when he imagines Gatsby’s final thoughts as a depressed consideration of the emptiness of symbols and dreams.