Quote 1
GOOD ANGEL
Faustus, repent; yet God will pity thee.
BAD ANGEL
Thou art a spirit; God cannot pity thee.
FAUSTUS
Who buzzeth in mine ears I am a spirit?
Be I a devil, yet God may pity me;
Yea, God will pity me, if I repent.
BAD ANGEL
Ay, but Faustus never shall repent.
FAUSTUS
My heart is hardened; I cannot repent.
Scarce can I name salvation, faith, or heaven. (2.3.12-18)
Well here's one theory of the way Predestination works, and one that doesn't deny the possibility of repentance and forgiveness. God will forgive the repentant, goes the theory, but only those who are predestined to repent will do so. Quite the Catch-22, eh? Faustus says his heart is "hardened," which means he cannot repent. A Calvinist would see this as evidence that he is indeed predestined for Hell. Well at least we got that cleared up.
Quote 2
LUCIFER
Christ cannot save thy soul, for he is just.
There's none but I have interest in the same. (2.3.85-86)
It's true that, in the theology of Christianity, Christ can't save the souls of those who have given up all hope for salvation. But it's not clear that Faustus has. Lucifer is being a bit sneaky here, using his words as a ruse to push Faustus over the edge so he'll seal his own fate.
Quote 3
BAD ANGEL
Go forward, Faustus, in that famous art
Wherein all Nature's treasure is contained. (1.1.72-73)
Although by referring to "Nature's treasure" the Bad Angel seems to be holding out the promise of wealth to Faustus, he could also be referring to the knowledge of Nature. Medieval and Renaissance scholars often described Nature as a book whose secrets could be discovered by the careful reader.