When Myrtle is killed by a passing car, her husband becomes rather extremely distressed. George Wilson is overcome with grief, anger and confusion. In this state he confuses the eyes of Dr. T.J. Eckleburg for the eyes of God, saying that God sees what is happening.
His neighbor tries to tell him that the eyes are simply an advertisement, but Wilson persists.
“God sees everything,” repeated Wilson.
Wilson implies that retribution is bound to come for the people who have killed his wife because the eyes of God have seen what happened. The guilty will be punished.
This notion serves to explain Wilson's actions as he tracks down Jay Gatsby and kills him. Wilson believes that he is carrying out a divine vengeance.
The eyes on the billboard are thus associated directly with the notion of an omniscient God (one that will enforce retribution for moral transgressions).
It could be argued that F. Scott Fitzgerald himself fully intended Dr. T. J. Eckleberg to be a symbol of God. If so, then God, like everything else in this vast junk pile, has been thrown away. God is dead. That would seem to be Fitzgerald's explanation for the way most of his characters behave in the novel. They indulge in orgies, like those depicted in the descriptions of Gatsby's parties. They lead meaningless lives, like Tom and Daisy Buchanan, and like Myrtle's sister and friends in New York. They commit adultery. They are involved in criminal activities which could easily involve murder.
God is dead in at least two ways in Fitzgerald's symbolism. In the first place, He has been thrown out and is like a ghost on the junk heap. Furthermore, the doctor who paid to have his eyes shown on a billboard is evidently not only no longer in practice but probably so old that he has died himself. It might be added that doctors in those days, and probably still in our days, did not advertise because it was considered unprofessional. Dr. Eckleberg must be an optometrist who is not a real doctor, in the sense that he cannot do most of the things an ophthalmologist can do, including prescribing drugs and performing eye operations. According to this interpretation of the symbolism of Dr. Eckleberg as God, if Eckleberg is defunct and never was a doctor in the first place, then God is dead and never was real even when almost everybody believed in Him.
The name Eckleberg seems to suggest that Dr. Eckleberg was Jewish. The God in the both the Old and New Testaments is also a Jewish god. It would be strikingly appropriate that George Wilson should see what nobody else has seen among all the people going past that board in both directions every day. . One of the reasons that the narrator Nick Carraway decides to return to what was called the West in those days, although it is now called the Midwest, may be that many more people in the Midwest still believe in God, still go to church, and still read the Bible.
Older people were shocked and many were horrified by what went on in the Roaring Twenties. This was largely because the older generations had been conditioned to believe in a code of morality that was solidly based on belief in the God whose is taken for granted throughout the Bible from "Genesis" to "Revelations." What they saw younger people doing was in direct violation and total disregard of some of the precepts of traditional religion. The younger people who were indulging in sinful behavior must have thrown God on the junk heap. Dr. Eckleberg, as God, still sees everything but can do nothing about it.
Well he was on a billboard looking down like God looks down on us. His eyes were faded to sybolize that God was not very popular at the time.
Since he is the doctor he is watching out for people just like God does from heaven or where ever you think he is.