It is a story parallel to what is happening in the Usher house.
The palace in the description represents Roderick Usher, whose hair used to be blond, as the yellow banners that wave in the air; through his eyes (the windows of the palace), a harmonious mind could be perceived, and wise words used to flow from his mouth, described as a door of pearl and ruby. However, gloom befalls on Roderick; his hair turns gray, his eyes are reddened by tears, his thoughts are discordant, and his mouth utters only the wild laughter of a madman.
Carpe Diem common meaning is "seize the day", which means that you must enjoy the day and maximize every moment as if it were the last. The idea is to have a productive well-lived day.
The phrase is in Latin, and was termed by the Roman poet Horace in his novel "Odes".
The "Nymph's Reply to the Shepherd", written by Sr. Walter Raleigh, refers to a young female nymph happy vision of life. For her, a true relationship must be based on loyalty and commitment, not like the shepherd's materialistic vision.
The nymph is always looking for something permanent that makes her happy, to "seize the day", even though they would be like dreaming: to be forever young, permanent happiness and true love.
What she means is that she really dreams of a joyful life with the shepherd on her side, but she realizes that he cannot afford her that because of his different and materialistic vision of life.
5--all of the other sentences are details relating to this main point.
