The Raven: Symbolizes death, and the reminder of death
December: Represents the cold harsh winter, where nothing lives
Night's Plutonian Shore: Pluto is the god of the underworld, this is another symbol for death
Lenore: The tragic, haunting loss of a woman
Basically all of these symbols and many more in The raven stand for death and add a haunting and depressing effect to the story. So they are used for emphasis
