A big motivator for Faustus's handing his soul over to the devil is his that he's jonesing for some power, big time. But here's the rub: in order to gain that power, Faustus has to give it all away—to Lucifer. Ultimately, the power Faustus dreams of could never be his. The power to rule not just men but all of creation belongs only to God in the world of Doctor Faustus. But the not-so-good doctor is not the only one in the play who has such high ambitions. Pope Adrian, too, uses his power to make all the world "stoop" (3.1.158). And we know that Lucifer fell from heaven because of his lust for power. So the Pope and Faustus are probably destined to wind up right where Lucifer is—in hell.
Faustus must give away power in order to gain it.
Faustus's desire for god-like powers destines him for hell long before he ever signs a contract with Lucifer. The contract is just a symptom of a larger problem.