Final answer:
The narrator in Poe's story shows readers his state of mind to emphasize the theme of hopelessness and the belief in the doomed nature of humanity.
Step-by-step explanation:
The narrator in Poe's story shows readers that he is in this state of mind to convey the theme of hopelessness and the belief that humanity is doomed. Through the use of mirror reflections and imagery, Poe intensifies the bleakness and despair in the story. The dilapidated house, the deteriorated state of Roderick Usher, and the reflection in the tarn all mirror the protagonist's state of mind and the impending death of Usher. By depicting the narrator as being from a world of hope and faith, Poe emphasizes the contrast between that world and the world of Usher.