The valley of ashes is a symbolic geographic location in the work. We can associate the rotting garbage and pollution of the valley with the moral corruption of many of the main characters. The valley of ashes is the setting for Myrtles death, which is the culmination of many wrongdoings by many characters.
The eyes of Dr. T.J. Eckelberg that George stares toward is representative of God looking down at the moral decay that has transpired. While Fitzgerald makes mention of this symbol repeatedly, it appears that the presence of God in the lives of the characters in the valley is absent.
To me, the fact that Michaelis can't find out where George Wilson goes to church says something about Wilson when you combine it with later stuff in the chapter. Later in the chapter, George talks about how he has told Myrtle that she cannot fool God. So George is invoking God, but he does not even go to church.
To me, this shows George as something of a weak man and a hypocrite. He is telling Myrtle she needs to adhere to this morality but he does not even really care enough about it to belong to a church.