In "The Masque of the Red Death", why do Prince Prospero and his guest lock themselves into an abbey?

Prince Prospero secludes himself and his high-ranking friends in order to escape a plague.

The story begins by introducing and describing the effects of the plague, called the Red Death. It is said to be unusually deadly and gruesome, named in part for the fact that one of its symptoms is profuse bleeding from one's skin, followed by death within half an hour.

Prospero is a ruler of some amount of land (it isn't specified) and when half of his citizens have died to the plague, he decides to seclude himself and a thousand nobles within a provisioned abbey, and lock themselves inside. They intend to ignore the outside world, justifying that it can fend for itself, and wait out the plague by diverting themselves with wine, entertainment, and a generally hedonistic lifestyle. 

At the conclusion of the story, Prospero and everyone else dies due to the intrusion of a physical personification of the Red Death, metaphorically suggesting that death cannot be eluded or ignored.