Honesty (or the lack thereof) stands at the heart of The Great Gatsby, and it is manifested and denied in several different ways through the several different characters. Let's reflect on that more deeply.
Nick Carraway claims to be an honest person, and for the most part, he is, except of course, to himself. He moves to New York seeking something, some kind of prosperity, some kind of pleasure, something new and different. He is caught up in a dream, a fantasy, yet he really doesn't want to admit it. Further, Nick claims that he is impartial, that he speaks truth, yet he judges people just as much as everyone else does on incomplete evidence and gets caught up in Gatsby's glamor. As such, he deceives himself.
Let's think about some of the other characters in the novel. Gatsby himself is living a lie. He is involved in plenty of shady dealings beneath his glamorous lifestyle. He has risen to the top, but his life is empty. He is not happy, not really fulfilled in his life. He seems to live above other people, to be disconnected with them, yet he is no better than they are. In fact, in some ways he is worse, for he does not care much about others, except of course, for Daisy. Even here, Gatsby lies to himself. He has convinced himself that Daisy loves him, not Tom, and he will not admit that she could ever love another man. Further, in an out-and-out lie, Gatsby determines to take the blame for Daisy when she hits and kills another person with the car. We might wonder if Gatsby has any real notion of truth.
Daisy, too, tends to live in a fantasy world. She's beautiful and wealthy, and she seems to be the perfect woman, yet she is not. She cheats on her husband. She is selfish and materialistic. Gatsby is her dream, but he is a false dream, for he is not what he seems to be.
Tom is a pretty nasty fellow who tends to live in the past, in the dreamworld of his glorious football hero days. He is cruel, unfaithful to his wife, idle, and selfish. He lives life on his own terms, not caring about anyone else.
Jordan, according to Nick, is “incurably dishonest.” She is also cynical and puts on a show to hide her own emotions, lying rather than facing the reality about herself and her relationships. She wants attention, but she doesn't know the right away of getting it.
We can see, then, that lies, deception, and skewed dreams drive the plot of this story and contribute greatly to the development of each of the main characters, who are all guilty of plenty of dishonesty. In terms of the Catholic worldview, we might note that this novel shows the exact opposite of the reliance on truth that stands at the heart of Catholicism. The characters in this story do not know God, and they are not in tune with the truth. They live for themselves rather than for God and others, and they are miserable because of it.