| Quote #1
The "Red Death" had long devastated the country. No pestilence had ever been so fatal, or so hideous. (1)
Poe tells us about the Red Death in the very first line of the story. In other words, we (the readers) are immediately confronted by the threat of death. We're made to feel that it's everywhere – the Red Death is all over the countryside, and has been for a while. And we're also made to feel particularly afraid of death, because the Red Death is "hideous" – it's a horrible way to die.
| Quote #2
The scarlet stains upon the body and especially upon the face of the victim, were the pest ban which shut him out from the aid and from the sympathy of his fellow-men. (1)
Death is isolating. Although one would hope for care and sympathy when one is dying (particularly if it's painful), the Red Death is so fearful that once somebody's caught it he's basically on his own. This loneliness adds to the scariness factor.
| Quote #3
All these and security were within. Without was the "Red Death." (2)
A sharp line is drawn here between a world of life and a world of death. Inside Prospero's abbey there's safety, enjoyment, good times. Outside, there's death. Even though the people inside are supposedly protected from death by being in the abbey, there's something unnerving about the image. Effectively, they're trapped inside, with death all around them.