Our narrator's a serious guy with a serious passion for his dead wife. His description of Ligeia, which opens the story, is as heartfelt as it is rosy. His love for Ligeia is obvious, but so is his commitment to understanding her. This same sort of balance, between serious contemplation and intense emotion, is key to the tale. It applies as much to the narrator's feelings about Ligeia as it goes to the structure of the story itself. Just as the narrator is overcome by his devotion to Ligeia yet struggles to understand her, we as readers have to deal with our own emotional responses – fear, for instance – as we try to look beyond the spooky bits. Poe is writing a story that is just as much about passion and power – what other words can better describe the force that animates Ligeia? – and the philosophical explanation for her return from the dead, as described by Glanvill.
Poe complicates the issue even more by making his narrator a little less than objective: his statements are colored by love and opium, and so the story takes on a sort of misty quality. So even as Poe is striking a balance, he's making sure it's an unsteady one.