The Jews regarded Michael as the special protector of Israel, and in Christian usage he became the protector of the church.
He is referred to in Apocalypse (12:7 to 9:): “And there was war in heaven. Michael and his angels fought against the dragon… And the great dragon was cast out, that old serpent called the Devil and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.”
The powerful prayer below was instituted by Pope Leo XIII and used to be said after every Mass in the old days.
“Holy Michael the Archangel defend us in the day of battle; be our safeguard against the wickedness and snares of the devil.
May God rebuke him we humbly pray; and do thou O prince of the heavenly host, by the power of God, thrust down to hell Satan and all wicked spirits, who wander through the world seeking the ruin of souls.”
St. Michael’s feast day is celebrated on Michaelmas Day, September 29th along with that of Saints Gabriel and Raphael.