| Quote #1
But the Prince Prospero was happy and dauntless and sagacious. When his dominions were half depopulated, he summoned to his presence a thousand hale and light-hearted friends from among the knights and dames of his court, and with these retired to the deep seclusion of one of his castellated abbeys. (2)
This description jars completely with the preceding paragraph about the Red Death "devastating the countryside." Prospero and his friends don't seem to care one bit. They're feeling "happy," "hale," and "light-hearted." They just want to keep having a good time, and refuse to take death at all seriously: the classical image of folly.
| Quote #2
The abbey was amply provisioned. With such precautions the courtiers might bid defiance to contagion. The external world could take care of itself. In the meantime it was folly to grieve, or to think. (2)
The use of "folly" in this spot is ironic. Isn't it ridiculous to believe it's folly to think? Yet that's exactly what Prospero's followers advocate, because if they spent time thinking, instead of enjoying themselves, they would be troubled.
| Quote #3
The Prince had provided all the appliances of pleasure. There were buffoons, there were improvisatori, there were ballet-dancers, there were musicians, there was Beauty, there was wine. (2)
Among the "appliances of pleasure" that Prospero packs his palace with are two classic symbols of foolishness: wine, and buffoons (also called "fools"). It's interesting that they're mixed in with the "high" arts.