s eternal "body and soul" to Lucifer in exchange for whatever he might ask or demand of Mephistophilis. To this end, Mephistophilis will do whatsoever he must by whatever means to balance out Faustus' mortal soul against the Doctor's earthly desires.
Shakespeare's villain, Iago -- to some the ultimate villain in all of Shakespeare's works -- is an evil who's sole purpose, real or imagined, is not preservation but the destruction of his master, Othello.
Thus, one evil seeks to maintain a status quo -- because that's his job -- while the other (perhaps because he hates his job so much) seeks to destroy the status quo.
In Faustus, the appearance of the good and bad angels are Marlowe's device to bring public the Doctor's thoughts. As W. W. Greg has said in "The Damnation of Faustus":
Faustus, of course, is for ever repenting -- and
recanting through fear of bodily torture and death --
and the Good and Bad Angeles, who personate the two
sides of his human nature, are forever disputing the
...