The collect for today, the Feast of Saint Michael and All Angels, from The Book of Common Prayer  (Canadian, 1962):
O EVERLASTING God, who hast ordained and constituted the services of Angels and men in a wonderful order: Mercifully grant, that as thy holy Angels alway do thee service in heaven, so by thy appointment they may succour and defend us on earth; through Jesus Christ our Lord. Amen.
The archangel Michael first appears in the Book of Daniel, where he is described as “one of the chief princes ” and as the special protector of Israel . In the New Testament epistle of Jude (v. 9), Michael, in a dispute with the devil over the body of Moses, says, “The Lord rebuke you “. Michael appears also in Revelation (12:7-9) as the leader of the angels  in the great battle in Heaven that ended with Satan and the hosts of evil being thrown down to earth. There are many other references  to the archangel Michael in Jewish and Christian traditions.
Following these scriptural passages, Christian tradition has given St. Michael four duties: (1) To continue to wage battle against Satan and the other fallen angels; (2) to save the souls of the faithful from the power of Satan especially at the hour of death; (3) to protect the People of God, both the Jews of the Old Covenant and the Christians of the New Covenant; and (4) finally to lead the souls of the departed from this life and present them to our Lord for judgment. For these reasons, Christian iconography depicts St. Michael as a knight-warrior, wearing battle armor, and wielding a sword or spear, while standing triumphantly on a serpent or other representation of Satan. Sometimes he is depicted holding the scales of justice or the Book of Life, both symbols of the last judgment.
Very early in church history, St. Michael became associated with the care of the sick. The cult of Michael developed first in Eastern Christendom, where healing waters and hot springs at many locations in Greece and Asia Minor were dedicated to him. Michael is supposed to have appeared three times on Monte Gargano , southern Italy, in the 5th century. The local townspeople believed that Michael’s intercession gave them victory in battle over their enemies. These apparitions restored his biblical role as a strong protector of God’s people, and were also the basis for spreading his cult in the West.
The Feast of St. Michael & All Angels is also known as Michaelmas. The Roman Catholic Church celebrates today as the Feast of Sts. Michael, Gabriel, and Raphael, Archangels.
Artwork: Tintoretto, Battle of the Archangel Michael and the Satan, c. 1590. Oil on canvas, Gemäldegalerie Alte Meister, Dresden, Germany.