Why has the narrator gone to visit Usher?

Usher is an old friend of the narrator's. Usher has been in ill health and the narrator has gone to visit him and, perhaps, cheer him up,

Its proprietor, Roderick Usher, had been one of my boon companions in boyhood; but many years had elapsed since our last meeting. A letter, however, had lately reached me in a distant part of the country — a letter from him — which, in its wildly importunate nature, had admitted of no other than a personal reply.