Themes are the fundamental and often universal ideas explored in a literary work.
Volpone's satire is directed against "avarice," which can be thought of as greed that extends not just to money but also to all objects of human desire. The play's main thesis is stated by Volpone himself, "What a rare punishment / Is avarice to itself." The punishment—and the central irony of the play—is that while greed drives the search for money, power, and respect, it ends up making everyone in the play look foolish, contemptible, and poorer, both spiritually and financially. A similar idea is stated by both Celia, when she asks in III.vii, "Whither [where] is shame fled human breasts?" and by the judge at the end of the play in his plea that the audience should "learn" from the play what happens to those who succumb to greed, emphasizing that the play's stance on greed is a didactic one, intended to teach the audience what greed's real consequences are. Volpone himself starts out as an instrument of this lesson—he dupes the Corvino, Corbaccio and Voltore into parting with their goods in the hope of inheriting his—but ends up an object of the lesson as well, for succumbing to his greedy want for sensual pleasure.
The Power of Stagecraft
There is a dichotomy in the play, never entirely resolved, between the devices of stagecraft and the conveyance of moral truth. In other words, there is a tension between the play itself (a play which, Jonson hopes, will be of moral value to those who see it) and what goes on in the play, in which the devices of stagecraft that are involved in the play's actual production are a source of deceit, confusion, and moral corruption. In other words, Volpone does not merely lie, nor he does not merely deceive; he makes an entire production out of his game, using a special eye ointment to simulate an eye infection, creating a character (the sick Volpone) using wardrobe, make-up, and props. He too seems to share the intention to expose moral folly, with the playwright, Jonson; but this is in the end seen to be another illusion. Likewise, Mosca and Voltore put on a production to convince the judges of their innocence. They use rhetoric and poetry to tell a story, complete with a shocking "surprise witness" and the graphic use of imagery (the appearance of "impotent" Volpone). The play thus exposes us to many different forms of theatrical illusion as methods of lying, perhaps in the hope of allowing us to better discern which forms of theater are sensationalistic, unhelpful, and inaccurate in their portrayal of reality.
"Everyone's a parasite" to paraphrase Mosca (III.i), and over the course of the play he is proved right, in the sense that everyone tries to live off of the wealth or livelihood of others, without doing any "honest toil" of their own. Corvino, Corbaccio and Voltore all try to inherit a fortune from a dying man; and Volpone himself has built his fortune on cons such as the one he is playing now. Parasitism, thus portrayed, is not a form of laziness or desperation, but a form of superiority. The parasite lives by his wits, and feeds off of others, by skillfully manipulating their credulity and goodwill.