Let's check in with Faustus and his magical men after dinner.
Faustus draws a circle and begins an incantation to call the spirit Mephistopheles.
When Mephistopheles shows up, Faustus thinks the little devil is just too ugly. He wants him to leave and come back when he looks more like a friar. For real.
When Mephistopheles has finished following these orders, he asks Faustus, whaddya want?
Faust commands Mephistopheles to serve him while he lives, but that's a bit of a problem. See, Mephistopheles has to get the a-okay from Lucifer, whom he serves first and foremost.
Whatever Faustus thinks happened, Mephistopheles assures him that Lucifer did not allow him to appear before Faustus; rather, the devils always gather around a person who blasphemes like, oh, Faustus, in the hopes of winning that person's soul away from God.
Ah, but guys, Faustus is already the devil's servant, and he's not a lick scared of damnation because in Hell, he'll get to chat it up with the pagan philosophers. Yeah, that sounds like a great afterlife…
Now it's time for the lowdown on the devil hierarchy. See, according to Mephistopheles, Lucifer is the highest-ranked devil. He was once an angel of God but fell on account of his pride. (See Paradise Lostif you want Milton's version of events.)
Then Lucifer joined up with all the other devilish spirits in a conspiracy against God.
That means that Mephistopheles is always in hell, no matter where he goes, because he's always separated from God and the joys of heaven.
Instead of, you know, listening to the guy, Faustus just mocks Mephistopheles for being so upset about having lost salvation.
Since he has already damned himself by blaspheming, Faustus has already made up his mind. The deal is sealed.
He wants to surrender his soul to Satan in exchange for twenty-four years on Earth with Mephistopheles as his servant.
Mephistopheles leaves to take Lucifer this message and a very excited Faustus beams at the thought of all the power he'll have, once he hands over his soul.