This story, one of Fitzgerald's most famous and critically-acclaimed, is an effective social commentary upon wealthy society. Fitzgerald experienced sudden wealth via his success selling stories to magazines, and his life as a writer was characterized by exposure to the upper echelon of society, who became frequent subjects and targets of his work. But his own entry into that world proved elusive, particularly his negative experiences in prep school, which are rather thinly-disguised in "The Diamond as Big as the Ritz." John Unger's character has a fair bit in common with Fitzgerald, and thereby becomes a fitting figure for the story's social satire elements. His origins in Hades are the subject of jokes by his new classmates and their families ("Is it hot enough for you there?") and his provincialism is occasionally the source of embarrassment, particularly when he visits Percy's home.
But despite John being a subject of ridicule, the story emphasizes John's humanity and compassion as measured against the Washingtons, who have had to become ruthless and somewhat cold-blooded in order to protect their wealth. In this way, the story functions as satire when it is made abundantly clear that the "good breeding" of the Washington family, obviated by their ostentatious wealth, is in reality an expression of selfish and narcissistic impulses whose main purpose is to guard the secret of their wealth at all costs.