From the Treasury of Daily Prayer:
The name of the archangel St. Michael means “Who is like God?” Michael is mentioned in the Book of Daniel (12:), as well as in Jude (v. 9) and Revelation (12:7). Daniel portrays Michael as the angelic helper of Israel who leads the battle against the forces of evil. In Revelation, Michael and his angels fight against and defeat Satan and the evil angels, driving them from heaven. Their victory is made possible by Christ’s own victory over Satan in His death and resurrection, a victory announced by the voice in heaven: “Now the salvation and the power and the kingdom of our God and the authority of His Christ have come” (Revelation 12:10). Michael is often associated with Gabriel and Raphael, the other chief angels or archangels who surround the throne of God. Tradition names Michael as the patron and protector of the Church, especially as the protector of Christians at the hour of death.
From The Lutheran Witness
What is Michaelmas?
In the Western church, St. Michael and All Angels has been celebrated since the 12th century. At the time of the Reformation, the Lutherans revised the celebration of former holidays and saint days in order to give greater prominence to the work of Jesus. St. Michael and All Angels was retained in the Lutheran liturgical calendar because it was seen as a principal feast about Christ. In fact, Philip Melanchthon, a colleague of Dr. Martin Luther, even wrote a hymn about St. Michael and All Angels (LSB 522, “Lord God, To Thee We Give All Praise”).
At first, this might strike us as strange. How is a feast named after an archangel about Jesus? But as with all commemorations within the Lutheran Church, the focus is not on the person but held in grateful thanksgiving to our Lord for using this person (or His holy angels) to give glory to His name and to bring about salvation for His people. The event celebrated on the Feast of St. Michael and All Angels is thus important both in regard to our salvation and to the comfort it brings the Christian conscience.
via The Lutheran Church – Missouri Synod – The Lutheran Witness.