Quote 4
FAUSTUS
"Faustus gives to thee his soul." O, there it stayed!
Why shouldst thou not? Is not thy soul thine own? (2.1.65-66)
The question of whether or not man's soul belongs to him is actually a question about Predestination in disguise. Does a man have free will to choose whom he'll serve, or does his soul already belong to God or the Devil from the moment he is born?
Quote 5
FAUSTUS
[...] Dost thou think that Faustus shall be damned?
MEPHISTOPHELES
Ay, of necessity, for here's the scroll
In which thou hast given thy soul to Lucifer. (2.1.124-126)
Here again, we see Faustus not quite convinced that his fate is sealed. Mephistopheles is all, um, dude, you wrote it down in your own blood. But Faustus gave his soul to Lucifer, which means it was a conscious choice. So if Faustus made that choice, what's to stop him from making a different choice later on? Backsies?
Quote 6
FAUSTUS
O thou bewitching fiend, 'twas thy temptation
Hath robbed me of eternal happiness.
MEPHISTOPHELES
I do confess it Faustus, and rejoice.
'Twas I that, when thou wert i'the way to heaven,
Dammed up thy passage. When thou took'st the book
To view the Scriptures, then I turned the leaves
And led thine eye. (5.2.92-96)
In a strange change of heart, Mephistopheles now takes the blame for Faustus's damnation. Did Faustus ever have a choice about his salvation? Or was Mephistopheles pulling the strings all along? This passage, like all the ones that came before it, leaves the answer unclear. P.S. Also notice the neat wordplay in line 94: Mephistopheles has "dammed up" Faustus's passage to heaven (as a beaver builds a dam), and this has damned him. Ba-dum ching.