MEPHASTOPHILIS: Why this is hell, nor am I out of it.
Think’st thou that I, who saw the face of God,
And tasted the eternal joys of heaven,
Am not tormented with ten thousand hells
In being deprived of everlasting bliss?
O Faustus, leave these frivolous demands,
Which strike a terror to my fainting soul.
FAUSTUS: What, is great Mephastophilis so passionate
For being deprivèd of the joys of heaven?
Learn thou of Faustus manly fortitude,
And scorn those joys thou never shalt possess.

This exchange shows Faustus at his most willfully blind, as he listens to Mephastophilis describe how awful hell is for him even as a devil, and as he then proceeds to dismiss Mephastophilis’s words blithely, urging him to have “manly fortitude.” But the dialogue also shows Mephastophilis in a peculiar light. We know that he is committed to Faustus’s damnation—he has appeared to Faustus because of his hope that Faustus will renounce God and swear allegiance to Lucifer. Yet here Mephastophilis seems to be urging Faustus against selling his soul, telling him to “leave these frivolous demands, / Which strike a terror to my fainting soul.” There is a parallel between the experience of Mephastophilis and that of Faustus. Just as Faustus now is, Mephastophilis was once prideful and rebelled against God; like Faustus, he is damned forever for his sin. Perhaps because of this connection, Mephastophilis cannot accept Faustus’s cheerful dismissal of hell in the name of “manly fortitude.” He knows all too well the terrible reality, and this knowledge drives him, in spite of himself, to warn Faustus away from his t-errible course.