What is the central conflict in "The Masque of the Red Death"?

The central conflict in "The Masque of the Red Death" is
between the nobles of the country, especially Prince Prospero, and the "red death," a
disease very much like the "black death" or plague that actually devastated late
medieval Europe. 

Prince Prospero is wealthy and powerful
and tries to escape the plague by quarantining himself and his nobles in a vast abbey.
This was something some of the nobles did during the black death, but it is not the act
of a just or benevolent ruler; as a ruler, one should not abandon one's subjects to
death while ensuring one's own personal safety.

Despite the
precautions to quarantine himself and his nobles so that they cannot be affected by the
plague, Prospero is followed into the abbey by the plague. Poe
states: 

And
now was acknowledged the presence of the Red Death. He had come like a thief in the
night. And one by one dropped the revellers . .
.

This conflict and its
phrasing is based on a biblical passage:

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The day of the Lord so cometh as a thief in the
night. For when they shall say, Peace and safety; then sudden destruction cometh upon
them, ... But ye, brethren, are not in darkness, that that day should overtake you as a
thief. (1 Thessalonians
5:2)

This parallel suggests
that death will always win the conflict, and that no matter how safe we are externally,
we are by nature mortal. However, Christians believe that death for the saved is the
beginning of eternal life, and thus within a medieval Christian context (the setting of
the story), by his own selfishness in trying to avoid physical death, Prospero not only
failed to avoid the plague but also sacrificed his chance at
Heaven.