Michael has to fight against Samael. In Jewish tradition, Samael is called “Samael the wicked, the head of all the devils.” Samael is the name of satan in Judaism.
He is represented as “the prince or advocate of Israel.”
The first encounter with satan is at the time of the fall. Michael fought satan when there was a war in heaven. When satan was thrown down from heaven, His enmity with Samael dates from the time when the latter was thrown down from heaven. Samael took hold of the wings of Michael, whom he wished to bring down with him in his fall; but Michael was saved by God.
According to rabbinical tradition, there are numerous times when Michael intervened in the history of the nation of Israel. Michael rescued Abraham. It was Michael who brought the message to Abraham that Lot had been taken captive. (Genesis 14:13) Michael protected Sarah from being defiled by Abimelech. He rescued Lot from the destruction of Sodom. He stopped Isaac from being sacrified. He saved Jacob in the womb. He protected Jacob from Laben. He wrestled with Jacob and later blessed him.
He saved Asenath, Dinah’s daughter from being killed. Tradition has it that Asenath later became the wife of Joseph in Egypt. He also saved Tamar from being burned. He was also said to have been the angle that destroyed the army of Sennacherib.
Thus St. Michael the Archangel is very much involved with the history of the nation of Israel.