You might have noticed a strange mingling of the fictional with the real in this story. Roderick’s artistic creations have a definite connection with what happens to the House of Usher. He paints an underground tomb; Madeline is entombed underground. He sings about the decline of a house; the House of Usher declines. He screams that the dead Madeline is standing at the door – and so she is at the door. In fact, way back the beginning of the story Roderick declares that will die from fear, which in fact comes true at the end of the tale.
One possibility is that Roderick, with his magic, lustrous eye, can foresee the future. He knows these events will transpire and so he prophecies them aloud. Another possibility is that Roderick actually causes these things to happen, so that he is consumed by fear he manifests his fear in reality, along with the help of some magic pixie dust from his haunted mansion.