Envy is a food of the mind, corrupting it with its poisonous juices and never ceasing to make it wretched and miserable at the prosperity and success of another. Institutes Book V, Chapter 21, St. John Cassian
The envious man tortures himself without cause, morbidly holding as he does, the success of another to constitute an evil for himself. Catholic Encyclopedia
For God formed us to be imperishable; the image of his own nature he made us. But by the envy of the devil, death entered the world, and they who are allied with him experience it. Wisdom 2:23-24
As the quotes above indicate, Envy is not just the desiring of another's goods, but the desire that the other be deprived of the goods. This is what makes it so insidiously horrible. It is not only covetousness, but an offense against charity, the highest of the virtues. One might think that the opposite of charity should be hatred, but envy contains a sort of hatred within itself, and is larger than hatred. It's possible to hate someone without wishing him ill, but it's impossible to wish ill to someone for whom we do not harbor some hatred.
There is a lot in the picture, some of which I don't understand, and some of which I can't make out due to the fact that there is a considerable amount of damage to the painting. For one thing, Envy appears to have grown horns. Is this just a symbol of evil, or is there something I'm missing?
Everything about Envy's face is hard and sharp--no softness allowed there. Her ears are large enough to hear any gossip that is in the air. Her word is like a poisonous snake that is meant to destroy others, but unexpectedly turns back to strike at her eyes, blinding her to the truth. Her head bears a distinct resemblance to that of Injustice, and just as Envy exceeds Injustice in evil, her face exceeds his in monstrousness.
Her left hand is a puzzle. It is in the shape of a claw, but the ends of her fingers do not seem to be there. Or are the claws sunk into the wall? Or as Andrew Ladis suggests in Victims and Villians in Vasari's Lives, have her fingers, "been reduced to mere nubs from all their clawing?" In her right hand she clings with all her might to a bag holding her possessions. No one will be able to get anything away from her! The Web Gallery of Art says that the decoration on her bag is a row of Turk's Head Knots, and the turban around her own head looks like one of these knots.
I wish I knew if there was some symbolism here.
Finally, she stands in flames that rise around her feet. Unlike those of Infidelity, which are off to the side, she is right in the middle. Is the fire a symbol of the inner fire of her jealously as the Web Gallery says, or are those the flames of Hell reaching up to consume her? Likely it's both.