Avarice means greed, and this play has a moral purpose, functioning to expose the folly of greed, not just the greed for money but the greedy desire to amass power and respect, not to mention to indulge sexual lust. Greed involves crossing the boundary beyond what is a reasonable desire and what is not. It indicates a willingness to hurt or be indifferent to the needs of others to gratify one own's desires. Greed, the play says, turns the moral universe upside down: instead of being most concerned with other people, the larger community, God or the advance of wisdom, avarice inspires us to use other people and our often faulty "knowledge" as tools to achieve our own desires, no matter how unreasonable those desires might be.
Volpone, a name which means sly fox, pretends to be ill, and others, hoping to become the heirs of his supposedly vast fortune, visit and bring him presents, not out of interest in him, but in hopes of the "pay off" of a large inheritance. Of course, they are only losing money in giving gifts, as Volpone is hardly going to die soon. Volpone, in turn, tries to seduce, then rape, Celia, the wife of another man, transgressing moral boundaries to satiate his own appetites. Volpone himself is so caught up in greed that he can't understand why Celia would not trade her virtue for the promise of money. The play sends a strong message to its audience: the pursuit of greedy desires is humiliating and dehumanizing. Further, avarice ironically backfires: people lose money, power and respect when they become obsessed with pursuing these goals at the expense of all else.
The entire play, from the opening act is based on the greed of the characters. Everyone is hoping to be the one to inherit Volpone's money and they are all angling to be the favorite friend.
A wonderful example is the behavior of Corvino towards his wife. He is so easily convinced to allow his wife to go and sleep next to Volpone in the hopes that it will not only help Volpone get better but will also curry further favor and get him closer to the inheritance. Obviously it is absurd and over the top, but it is a great example of greed overcoming any normal scruples.
The action continues, again with the main driving force being the greed of the characters.