"Don't you know that I am sane and earnest now; that I am no lunatic in a mad fit, but a sane man fighting for his soul?"Please explain this quote...

This is a quote from Renfield.  It is one that reflects
how the ideas of madness and sanity, love and hatred, passion and vengeance are all
morphed together throughout the narrative.  Renfied is thought to have been insane for
his mannerisms of eating bugs and his extreme devotion to his "master" of Dracula.  Yet,
it is only through Renfield's insights that the Vampire Hunters fully understand that
Mina has been bitten. At the same time, Renfield says this line in pleading to the
Vampire Hunters, Dr. Seward amongst them, that he can be saved and that he can be of
assistance to them.  His change might be a result of having seen Mina and understanding
Dracula's coveting of her.   Being institutionalized for being presumed as insane, when
Renfield calls out his sanity "fighting for his soul," it brings to light the idea of
how one must try in futility and vain to alter the perception society has of them.  On
one hand, intense emotions can cause individuals to believe one set of ideas.  Yet,
intensity does falter and does eventually expire, which might cause the same individual
to believe the opposite.  This dualism might be where the quote lies and why it is so
powerful given the dualistic dimensions in the work.