The speaker in The Great Gatsby is Nick. In the beginning of the novel Nick is a leisurely young man going with the flow of things but by the end he gets so caught up in it all he forgets about himself. An example of this would be "I just remembered that today's my birthday." (Fitzgerald 135) Nick is so consumed with what is happening between Gatsby and Daisy and Daisy and Tom that he forgets about himself. By the end of the novel he doesn't have to worry about Gatsby, Daisy, Tom, or Jordan but the experiences he had made him into a more mature version of himself.

The books purpose is to show people how materialism can consume your life and destroy relationships. This is shown when Nick says "They were careless people, Tom and Daisy- they smashed up things and creatures and then retreated back into their money or their vast carelessness, or whatever it was that kept them together, and let other people clean up the mess they had made."(Fitzgerald 179) He is describing how when you have money you feel as though you have power over others. With money comes greed and with greed comes the ability to do whatever you want and not care about who suffers. While this book is an entertaining love story I believe it was also written as a warning about the dangers of greed. 

The target audience for The Great Gatsby is romantics. They will be swept up in the story of how Gatsby loved Daisy so he sought after her for years. The fact that Tom is cheating on Daisy with Myrtle and they no longer share the love they once had adds even more to the story. However its the tragic irony when Daisy kills Myrtle in a car accident which will have them completely shocked. There is also a little bit of a connection between Nick and Jordan however that never goes anywhere until Nick ends the nothing they had. By playing with the feelings of the romantic he uses their emotions to keep them in suspense up to the end.
Fitzgerald sets a very mysterious mood. Throughout the novel you are introduced to new theories about Gatsby, some being true some fiction. It can sometimes be hard to tell what is fact about him which makes him a very mysterious character. Throughout the story Gatsby is mixed up in the events but because of your lack of knowledge of his past it makes for a suspenseful story.