Who is Dr. Abrenuncio, Dr. Abrenuncio de Sa Pereira Cao from Of Love and Other Demons and what is their importance?

Dr. Abrenuncio is of Portuguese Jewish origin, and considered a near heretic. He is a learned man and skilled doctor, though many people resent him because of his practices, such as predicting people's death date. Doctor Abrenuncio is brought in to treat Sierva, until the Marquis foolishly turns to other quack doctors.