Read the quote below and explain the following:
the platonic conception
the effect of the biblical allusion
the point about the nature of service
"the truth was that Jay Gatsby of West Egg, Long Island, sprang form his Platonic conception of himself. He was a son of God-a phrase which, if it means anything, means just that-and he must be about His Father's business, the service of a vast, vulgar and meretricious beauty."
After interpreting this comment, connect it to this quote from the introduction:
"What foul dust floated in the wake of his dream."
As the editor says above, your question has way too many parts for this forum. I'll just elaborate on one of those parts: the platonic conception.
"Conception" deals with Gatsby's creation of his persona, his current self. He is a self-made man financially, of course, at least as far as we know (his past is still somewhat mysterious). But other aspects of Gatsby are carefully crafted, too: his appearance, his reputation, his mysteriousness. Most of all, his love for Daisy and his memories of their brief love affair are carefully crafted.
"Platonic" refers to Plato's idealistic belief that the "perceptible world is an illusory shadow of some higher realm of transcendent Ideas or Forms." "Perceptible" means what is perceived, what is seen, and "transcendent" is a surpassing of usual limits; exceeding beyond usual human limits.
So Plato believed that the world we see was just an illusion, a shadow, of some idea or form beyond what we see.
So Gatsby's persona was created from his platonic view of himself: his view that his love for Daisy was more than normal, that it was transcendent, that it surpassed and exceeded usual human limits. He created himself, his image, his reputation, his plan to win Daisy back, etc., out of a belief that his love was special, and that the love between himself and Daisy was special.
Gatsby may have been correct about his love for Daisy, but unfortunately for him, he was incorrect about Daisy's love for him. And that, truly, leads to foul dust at the death of his dream.
(Definition of Platonism taken from The Concise Oxford Dictionary of Literary Terms)
This quote essentially means that Gatsby has a spiritual impression about his relationship with Daisy. He saw himself as being in service to her, as we are instructed by God to be in service to others... he just picked one particularly permissive, vulgar, selfish and vain young person to serve. The word platonic refers to spiritual, not sensual. The biblical allusion here refers to Jesus Christ who had a goal to serve his Father through serving others. Jay tries to be a savior to Daisy from her relationship with Tom. Daisy, just like mankind, doesn't particularly look for a savior...
Jay does seem to be one happy to service others as he throws big parties and buys dresses for women who get soiled as a result of being there.
The quote at the end might also be a biblical allusion. From dust we have come and to dust we shall return. Gatsby's quest for Daisy results in nothing but 3 deaths, and a weaker marriage. His dream of Daisy left a lasting wake of dust as 3 people died.
That's just my quick take. That was a question with way too many parts, but there's an attempt for you.