How is the significance of the seventh apartment revealed at the end of Poe's "The Masque of the Red Death"?

The significance of the eerie seventh apartment is revealed at the end of "The Masque of the Red Death" through Prospero's final confrontation with his uninvited guest.  The uninvited guest, who represents the embodiment of the Red Death itself, comes unknown and uninvited at midnight.  This shows us the significance of the ebony clock found in the seventh apartment.  Shrouded in burial robes and bathed in blood, the figure mirrors the apartment itself with its black tapestries and blood-red windows.  The eerie red light emanating from these windows automatically hits each inhabitant of the room, showing that none of the guests can avoid the effects of the Red Death.  Of course, it is within the chamber itself that the figure claims its first victim:  Prince Prospero.  This is quite ironic, considering it is Prospero himself who tried to cheat death by inviting all of his friends into his home in order to defeat the pestilence from the beginning.  Prospero confronts the figure and immediately falls down dead in the middle of the seventh apartment.  All of the other partygoers follow suit, finding that (as expected) the uninvited guest has no "tangible form."