Why has the devil befriended Faust and taken up a code of honor with him? Is he a special temptation?
Goethe creates his Faust as a special temptation to the devil in response to the prevalence of Enlightenment thinking in Germany during the eighteenth century. In "The Prologue in Heaven," God and Mephistopheles have made a bet (lines 312-7). Mephistopheles bets that he can convince the scholar that he can be the possessor of a god-like mind; that is, that all things are knowable. God believes he can convince him of the limits of human reason:
Mephistopheles: ....He serves you in a curious fashion.
Not of this earth the madman's drink of ration,
He's driven far afield by some strange leaven,
He's half aware of his demented quest...
The Lord: Though now he serve me in but clouded ways,
Soon I shall guide him so his spirit clears.
Enlightenment thinkers were fueled by new discoveries in science and the findings of explorers which broadened their worldviews. Enlightenment principles dictated that through the use of reason, progress was unending and all questions could be answered. Additionally, human aspirations, Enlightenment adherents believed, should focus solely on this life, not in any potential and unproven afterlife reward.
The devil knows that there are limits to human knowledge. But Faust, convinced that all things are knowable, falls for the promise, "I'll give you what no man has seen before," he says (1674). The best lies always contain a grain of truth.