Answer:
The nightingale was being contrasted with a singing-feathered creature, without a transgression.
nightingale is contrasted with great men though sparrow is contrasted with the terrible man.
Similarly great and terrible, men, Sweet or Bitter, or Satan.
Good Man-Is in every case great, feels and do great to other people, so I contrast Nightingale and a decent man.
Bad Man - Do just awful and poor things to his environment and to other people.
So sparrow is contrasted and an awful man.
