In "The Fall of the House of Usher," what were some of the themes that were explored in the novels that the narrator chose to read?
It is important to note that during the middle section of this excellent short story, the activities that Roderick Usher engages in all reflect his disturbed inner-nature and his troubled psyche. He produces paintings that are so abstract that the narrator is hardly able to describe them. He sings a song that, although it starts pleasantly enough, eventually brings in evil spirits that destroy the idyllic setting created by the lyrics and are clearly representative of Roderick's inner troubles and strivings. His choice of reading likewise represents his own character, as the narrator says:
Our books--the books which, for years, had formed no small portion of the mental existence of the invalid--were, as might be supposed, in strict keeping with this character of phantasm.
Thus Roderick devotes himself to various arcane tomes concerning such topics as forgotten religions and journeys of exploration, poring over abstract and recondite pieces of information that perhaps represent his own desire to work out what is happening to him and his sister. Thus the choice of reading material perhaps represents Roderick's own desire to make sense of his own situation and malady, and understand how and why the curse that he refers to has been brought down on him.