By saying that the other people think of him as mad,, that he is sick and that he hers things, from hell, and heaven, people will read this and think of him as mad, as gone crazy and he tries to defend himself from that afirmation.
The narrator of this excerpt complains that other people characterize him as insane (<em>"why will you say that I am mad?"</em>) and he wants to deny the credibility of this claim. He says that he might be nervous, but he is not mad. In fact, his senses are sharper than ever, as he can hear everything, including what goes on in Heaven and Hell. This fact, intended to convince us of his sanity, proves that he is indeed insane.
