He was bad in many ways, i.e. attempting suicide, consorting with the devil, doing black magic, wishing for perfect knowledge, etc., but how exactly was he good?
"Faust is a scholar and wizard whose good works as a university teacher and as a physician to the downtrodden have earned him heaven. He is proof that the world has worthy men. But Mephistopheles mocks Faust for his dedication to God and suggests that his ceaseless thirst for knowledge is a weakness that could cost him his eternal soul. The Lord concedes that Faust is in turmoil over his attempts to understand the deepest mysteries of the universe. But, the Lord says, “I will one day lead him to the place of heavenly light.” Taking that statement as a challenge, Mephistopheles wagers that he can bend the will of Faust away from God—presumably by providing him the knowledge he seeks—and thereby win his soul for all eternity.........It’s a bet. The Lord grants Mephistopheles permission to tempt Faust, saying that even in his darkest moment Faust will be conscious of the righteous path."
