Prince Prospero is selfish and cares more about the wealthy members of his kingdom than the general public. 

The fact that Prospero builds himself a castle and holes himself up inside of it with the wealthy constituents of his kingdom shows he has no interest in actually taking care of his people. He does not try to stop the plague or protect his kingdom from its devastating social and economic effects. He just flees. 

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. This was an extensive and magnificent structure, the creation of the prince's own eccentric yet august taste. 

The act of walling himself up inside the abbey and throwing a big party also shows Prospero is delusional. First of all, it is ridiculous to think they will be safe just because no one can get in or leave. Second, throwing a party is a terrible waste of resources when your people are dying. Prospero is in denial. 

Prospero’s decorating style is creepy and bizarre. The scariest part is the ebony clock, which chimes to seem like death itself. The revelers stop when they hear it.

But, in spite of these things, it was a gay and magnificent revel. The tastes of the duke were peculiar. He had a fine eye for colors and effects. He disregarded the decora of mere fashion. His plans were bold and fiery, and his conceptions glowed with barbaric lustre.

It turns out that you can't actually just build a spectacular abbey and escape death. Death finds Prospero anyway. He crashes the party in physical form. Prospero's selfishness catches up with him and his guests.

What do you learn about Prince Prospero from his desire and his attempt to keep his household free from the disease?

Half of the people in the Prince's "dominion" have been killed by the plague. But he is "happy and dauntless." Poe, the narrator, never mentions the Prince's attempts to fight the plague or help his people. Instead, he invites a thousand healthy ("hale") people from his court to isolate themselves from the public and the plague. These are people from his court: the nobility. So, here we have a prince who does not care for his people. His strategy is to protect himself and a select group from the upper class. This is the definition of elitism. To illustrate the prince's selfish thinking, the narrator adds, "The external world would take care of itself. In the meantime, it was folly to grieve, or to think." 

His company does not grieve for those suffering. And they do not hide in this fortress with humility and caution. Rather, they arrogantly party while those outside the walls are suffering. The prince's and his guests' arrogance is addressed when death (the red death) finds its/his way into their party. Their hedonism at this ongoing party shows their selfishness. The prince is proud. He does not sit inside those walls, humbled and thankful that he has not contracted the disease. Rather, he foolishly parties with his select friends. His cavalier attitude mocks death in general. The prince therefore mocks Poe's personified "death" in this story. Therefore, when the masked man (personifying death) gets to him, it is retribution and poetic justice. In other words, in his arrogance and selfish behavior, the prince is asking for it. 

In "The Masque of the Red Death," what does the reader learn about Prince Prospero from his desire and his attempt to keep his household free from the disease?

Prince Prospero's title and his ego match each other in the air of superiority. So superior does Prospero feel he is that he believes that he can stave off Death itself.

When his dominions were half depopulated, he summoned to his presence a thousand hale and light-hearted friends...to the deep seclusion of one of his castellated abbey [where] the courtiers might bid defiance to contagion.

This defiance of the prince is reflective of much haughtiness. For, at the abbey, Propero holds a masquerade of great splendor. Scoffing at the somberness of why they are assembled in the abbey in order to have a "magnificent revel" Prince Prospero has had each of the seven rooms furnished in different colors that have corresponding motifs. Thus, it seems as though dreams stalk from chamber to chamber; these dreams seem to traverse the rooms. This traversal of images and "arabesque figures with unsuited limbs and appointments" distorts the reality of what occurs, until the guests are confused. It is at this point of the blurring of the images between reality and distortion that the Red Death invades the abbey. The threatening picture is shrouded as though from the grave, like death. He is tall and gaunt-appearing, causing Prince Prospero to shudder with terror. Nevertheless, the arrogant prince challenges Death. But Prospero, who represents wealth and money, is no match for Death.