From The Office of Readings:
Whenever some act of wondrous power must be performed, Michael is sent, so that
his action and his name may make it clear that no one can do what God does by
his superior power. So also our ancient foe desired in his pride to be like God,
saying: I will ascend into heaven; I will exalt my throne above the stars of
heaven; I will be like the Most High. He will be allowed to remain in power
until the end of the world when he will be destroyed in the final punishment.
Then, he will fight with the archangel Michael, as we are told by John: A battle
was fought with Michael the archangel.