There is a very obvious irony in these lines. The narrator believes the audience will think that he is not mad when he describes the "concealment of the body." However, when he goes on to describe the dismemberment of the body, it proves quite the opposite of his sanity. It is apparent that although the narrator views himself to be "wise," he is just deranged and does not recognize the severity of his actions. Perhaps, he is wise to have taken care of the body like such, but to not "think [him] mad" is not what can be deduced from him cutting "off the head and arms and the legs" of another human being.

This line is interesting. The narrator personifies death, and more specifically, that he is "Death." The narrator believes he holds the man's life in his hands. Additionally, the narrator seems to see himself as inescapable, and that old man will die if Death wills it so. He has been stalking and watching the old man for eight nights and is ready to finally strike, moving in from the doorway. The "enveloped" victim's fate has already been sealed. As much as the old man tries to console himself, it is "all in vain" because Death has already enclosed him in darkness.