Doctor Faustus by Christopher Marlowe is a Morality play and many scenes from the play create biblical parallels. And we see Faustus quoting some lines from the following biblical text. These are:
The reward of sin is death. That's hard. (40)
If we say that we have no sin, we deceive ourselves,
and there's no truth in us. Why then, belike we…
must sin, and so consequently die.(45)
Note that Faustus doesn’t quote this biblical line perfectly. Faustus says that the reward of sin is death and since all men are sinners, without exceptions, all men must die. He misses out the next line due to which he overrules the possibility of repentance and forgiveness of man’s sins by the lord.
For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord. (From Romans).
If we say that we have no sin, we deceive ourselves and there's no truth in us. If we confess our sins, he is faithful and just, and will forgive our sins and cleanse us from all unrighteousness. (from first book of John).
Faustus is too intelligent a scholar to miss out this line by mistake. I think this tells us that though Doctor Faustus has read a lot, he has a shallow and limited understanding. He gives more importance to theoretical knowledge than divinity and wisdom. He ignores the forgiving nature of God or the truth of redemption in Christianity, and arranges these lines in a way that changes the entire meaning. This means, in actual sense, Faustus has a poor learning.