How we cite our quotes:
If we say that we have no sin,
We deceive ourselves, and there is no truth in us.
Why, then, belike we must sin
And so consequently die.
Ay, we must die an everlasting death.
What doctrine call you this? Che serà, serà?
What will be, shall be? Divinity, adieu! (1.1.41-47)
Shmoop calls this the Doris Day doctrine. But here's the thing. Faustus doesn't just think that mankind is predestined to sin, and is therefore headed to hell. He also thinks that, because of this, studying religion has no point. This tells us that Faustus is not interested in knowledge for its own sake—only for how it can benefit him. But the joke's on Faustus, because if he had studied religion, he probably wouldn't be in this predicament.
For, when we hear one rack the name of God,
Abjure the Scriptures and his Savior Christ,
We fly in hope to get his glorious soul;
Nor will we come unless he use such means
Whereby he is in danger to be damned. (1.3.45-49)
The idea that swearing—taking God's name in vain, or cursing God—draws devils around you who will to try to win your soul for the Dark Side, is not a new one. In fact, it dates back to medieval times (no, not the restaurant). Back then, folks thought that a person always opens a space in his heart for the devil when he sins, but by swearing, he announces it to the world, basically advertising to evil spirits that his soul is theirs for the taking.
Stay, Mephistopheles, and tell me
What good will my soul do thy lord?
Enlarge his kingdom.
Is that the reason why he tempts us thus?
Solamen miseris socios habuisse doloris. (2.1.38-41)
Mephistopheles's Latin response to Faustus's question translates into "to the unhappy it is a comfort to have had company in misery." (In other words, "misery loves company.") This is basically a warning from Mephistopheles to Faustus to turn back from his intended course of action, since it implies that hell is miserable. But Faustus ignores it. He's really good at ignoring people.