Devotion to Michael the Archangel is one of the oldest devotions of the Church.
Saint Michael in the Old Testament
St. Michael the Archangel is referred to by name rarely in the Old Testament, only in the book of Daniel – in 10:13 and 21, and again in 12:1:
"At that time shall arise Michael, the great prince who has charge of your people. And there shall be a time of trouble, such as never has been since there was a nation till that time; but at that time your people shall be delivered, every one whose name shall be found written in the book." - Dan 12:1
He was previously described but unnamed in the earlier book of Joshua 5:13-15:
When Joshua was by Jericho, he lifted up his eyes and looked, and behold, a man stood before him with his drawn sword in his hand; and Joshua went to him and said to him, "Are you for us, or for our adversaries?"
And he said, "No; but as commander of the army of the LORD I have now come." And Joshua fell on his face to the earth, and worshiped, and said to him, "What does my lord bid his servant?"
And the commander of the LORD's army said to Joshua, "Put off your shoes from your feet; for the place where you stand is holy." And Joshua did so.
However, traditions from both before Christ's coming and after, as well as the teachings of the Fathers of the Church, indicate St. Michael was honored as guardian angel of the people of God, and fulfilled the role of defender during the time of the patriarchs onward. The Fathers of the Church tell us that in many events throughout the Old Testament, the appearance and assistance of an unnamed angel is believed to be Michael, the archangel.
Devotion in the Early Catholic Church
As St. Michael was an advocate for the people of God in the Old Testament, he continues to be protector in the New Testament after the coming of Jesus. Devotion to St. Michael has been present in the lives of the Catholic faithful from the earliest centuries of the Church. As he was the advocate of the patriarchs in the Old Testament, and is believed by many eminent Doctors of the Church to have been the angel assigned to be with the Savior in His 33 years on earth, Michael is now considered the Guardian of the Blessed Sacrament. Due to the various events and miracles associated with St. Michael, Christian Tradition names to him the following four offices:
1. To fight against Satan.
2. To rescue the souls of the faithful from the Devil, especially at the hour of death.
3. To attend the dying and accompany them when facing the Almighty Father.
4. To be the champion of God's people; the Israelites in the Old Law, the Christians in the New Law; and to be Patron of the Church.