Honestly I would think he’s just drunk and surprised about the books. Or that Gatsby took his time to fill shelves with books and on how grand it is. Just in awe with the luxury I guess.
Answer:
The beginning of the story
It is likely that this passage is supposed to be placed at the beginning of the story. This is due to the fact that the passage deals with the beginning of the family's lineage. Moreover, the passage describes how the two gods had children, and how these children became the sky and the earth. We can conclude that the author believes this to be the beginning of the world.
It changes the meaning by saying oh cupids eyes are rolling like rolling ocean when they aren't.