What is the narrator's goal in "The Fall of the House of Usher?"

In The Fall of the House of Usher, the narrator is going to visit Roderick Usher, a friend of his from childhood. Roderick had sent him a letter, requesting that he come visit because Roderick was suffering from a malady and he hoped that the narrator would be able to make him feel better. 

When the narrator arrives at the House of Usher, he finds Roderick in an odd state, being affected by "a mere nervous affection". According to Roderick, his senses had heightened significantly enough that his eyes hurt from even the faintest light, all but a few sounds were far too loud, most textures were unendurably uncomfortable, scents were too much, and even the blandest tasting food was unbearable. Also, Roderick is suffering because his sister, Madeline, was on the verge of dying, and Roderick was distraught. 

In his attempt to make Roderick feel better, the narrator read or painted with him or listened to his music improvisations, trying to distract Roderick from his anxiety and misery. Unfortunately, the narrator was unsuccessful in the end, and the story ends with the House of Usher, along with Roderick and his dead sister, sinking into the lake as the narrator watches in horror.