In Scene XIV of Christopher Marlowe's Doctor Faustus, we meet Faustus speaking with two or three Scholars about the subject of "fair ladies". The Scholars had chosen Helen of Troy as the most beautiful woman "who ever lived" (although she is a mythological figure), and they ask Faustus to use his power to bring back Helen of Troy for them.
Helen of Troy is a lead figure of Greek mythology. The Greeks think of her as the most beautiful woman in the world. Legend says that she is the daughter of Zeus and Nemesis. Other versions of the same legend point Helen's mother as Leda, who was presumably raped by Zeus, producing Helen as one of her offspring.
In Homer's The Iliad , as well as in The Odyssey, Helen is the reason behind the Trojan War. This is because Helen is the wife of Menelaus, King of Sparta. Paris, a prince of Troy, elopes with her (it is not ascertained whether she was kidnapped or if she goes voluntarily) thinking that Helen is the beautiful gift that Aprhodite had promised him. This is what sparks the war.
After the message of the Old Man, we see Faustus realizing the extent of his folly and feeling despair. Mephistophilis reproaches him for his "disobedience" to Lucifer and lays renewed claim on his soul, "I arrest thy soul.". To prove his sincere intentions toward Lucifer, "with my blood again I will confirm / My former vow," he requests that Mephisto give him Helen as his "paramour."
Instead of by asking God or anything holy. Faustus makes his sin even greater by embracing Helen as his spiritual guide.
Sweet Helen, make me immortal with a kiss.[Kisses her.] Her lips suck forth my soul; see, where it flies!—Come, Helen, come, give me my soul again. Here will I dwell, for Heaven is in these lips, And all is dross that is not Helena.
Faustus inability to change his fate and accept the grace the Old Man says is with him makes him commit even further sins.
[Helen's] sweet embracings may extinguish clean
These thoughts that do dissuade me from my vow,
And keep mine oath I made to Lucifer.
Therefore, the entrance of the character of Helen of Troy is representative of the Renaissance ideal of revisiting all things Greek. This is illustrated in that Faustus, a Renaissance man himself, meets with scholars to speak of this very topic. However, Helen also represents Faustus's inner lust for knowledge and to power.
However, she also represents Faustus's struggle to keep to his agreement to renounce God and unite with Lucifer: he asks for her after being tempted to call on God's grace; after being chastised by Mephisto; after desperately agreeing to renew his vow; after begging for mercy from Lucifer. He asks for her as a way to distract his mind from calling on God's grace.