Why is it significant that Mephastophilis joins Fauntus on this journey?

Mephastophilis joining Faustus on his journey is significant because it symbolizes the internal struggle between ambition and moral consequences. As Faustus seeks knowledge and power through dark means, Mephastophilis serves as both a guide and a reminder of the pact's dire implications. This partnership highlights the themes of temptation and the quest for enlightenment, ultimately leading to Faustus's tragic downfall. Their relationship underscores the conflict between human desire and the spiritual repercussions of forsaking one's soul.