It is important first to understand the purpose of a morality play:
This type of play essentially depicted a battle between the forces of good and evil in the human soul.
A dramatic descendant of mystery and miracle plays of the medieval period, a morality play's purpose was to allegorically point out good and evil, and the dangers mankind faced in participating in sinful behaviors, and to highlight the cost of pursuing such immoral actions.
In Marlowe's Dr. Faustus, Faustus (a great scholar) grows bored with life, believing he has learned all he can of this world. So he summons Mephistopheles to make a deal with Lucifer to sell his soul to the devil for twenty-four years of service from Lucifer's demon. He tells Mephistopheles:
I charge thee wait upon me whilst I live,
To do whatever Faustus shall command... (I.i.38-39)
Even in the face of Mephistopheles' warnings of his experiences of hell...
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? (81-84)
...and Faustus' own misgivings, he goes ahead and makes his deal with Lucifer. In this one section, several thing are highlighted: mankind's inherent temptations, its natural goodness and wisdom that try to guard against committing grave sins, and mankind's persistence to have what it wants rather than pursue the more difficult path to fight that which it knows to be dangerous and/or wrong. Another concept comes from Mephistopheles: that hell is being absent from the presence of God and the glories of Heaven.
The story continues to describe Faustus' pursuits. He learns (as does the audience) of the "seven deadly sins," or sins that were seen by the Catholic Church as wrongdoings that could lead to eternal damnation, including: wrath, greed, sloth (laziness), pride, lust, envy and gluttony.
By the story's end, Faustus' time (the twenty-four years) have come to an end. Still there seems to be opportunity for Faustus to repent—and he has no doubt what lies ahead if he does not. However, he is so far removed from a state of grace (good-standing with God) that he says there is no hope for him, and he doesn't even bother to try:
But Faustus' offences can never be pardoned: the
serpent that tempted Eve may be saved, but not Faustus. (V.ii.15-16)
The Third Scholar (as do others) tells Faustus to "call on God." But Faustus replies:
On God, whom Faustus hath abjured! on God,
whom Faustus hath blasphemed! Ah, my God, I would
weep, but the Devil draws in my tears. (29-31)
The scholars learn of Faustus' deal with Lucifer and ask him why he did not ask them to pray for him. He notes that Lucifer threatened "to tear me to pieces if I named God," but certainly his fate when Lucifer takes him will not be any better: it seems just another excuse—which is yet another human character flaw in Faustus. He does not assume responsibility for his actions; he lacks faith; and, he does not believe in the power of God over evil.
Faustus rejects theology because of a misunderstanding of the relationship between divine justice and Christian mercy.
This is a morality play in that it uses Faustus' story and his fate to warn others of what will happen if they follow his immoral behaviors, and commit sins against God.