In Hebrew, Michael has the meaning "who is like God?". Archangel Michael is mentioned three times in the Book of Daniel, once as a "great prince who stands up for the children of your people". The idea that Michael was the advocate of the Jewish nation became so prevalent that in spite of the rabbinical prohibition against appealing to angels as intermediaries between God and his people, Archangel Michael came to occupy a certain place in the Jewish liturgy.

In the New Testament, it is Archangel Michael that leads Our Lords armies against Satan's forces in the Book of Revelation, where during the war in heaven he defeats Satan. In the Epistle of Jude Michael is specifically referred to as "the archangel Michael". Christian sanctuaries to Michael appeared in the 4th century, when he was first seen as a healing angel, and then over time as a protector and the leader of the army of God against the forces of evil. By the 6th century, devotions to Archangel Michael were widespread both in the Eastern and Western Churches.

Old Testament

In the Old Testament (and Hebrew Bible), prophet Daniel (in Daniel 10:13-21) experiences a vision after having undergone a period of fasting, whereby an angel identifies Michael as the protector of Israel. Daniel refers to Michael as a "prince of the first rank". Later on (in Daniel 12:1), in the vision Daniel is informed about the role of Michael during the "Time of the End" when there will be "distress such as has not happened from the beginning of nations" and that:

"At that time Michael, the great prince who protects your people, will arise."

In view of this, Archangel Michael is seen as playing an important role as the protector of Israel, and later of the Christian Church.

References to the "captain of the host of the Lord" encountered by Joshua (Joshua 5:13-15) in the early days of his campaigns in the Promised Land have frequently been interpreted as Michael the Archangel, but there is no theological basis for that assumption, given that Joshua then worshiped this figure, and angels are not to be worshiped. Some scholars also point that the figure may refer to God himself.

In the book of Joshua's account of the fall of Jericho, Joshua "looked up and saw a man standing in front of him with a drawn sword in his hand". When the still unaware Joshua asks which side of the fight the Archangel is on, the response was, "neither...but as commander of the army of the Lord I have now come".

New Testament

The Book of Revelation (12:7-9) describes a war in heaven in which Michael, being stronger, defeats Satan:

"...there was war in heaven. Michael and his angels fought against the dragon, and the dragon and his angels fought back. But he was not strong enough, and they lost their place in heaven."

After the conflict, Satan is thrown to earth along with the fallen angels, where he ("that ancient serpent called the devil") still tries to "lead the whole world astray".

Separately, in the Epistle of Jude 1:9 Michael is specifically referred to as an "archangel" when he again confronts Satan

"Michael the Archangel, when contending with the devil he disputed about the body of Moses"

A reference to an "Archangel" also appears in the First Epistle to the Thessalonians 4:16

"... the Lord himself shall descend from heaven, with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first" (American Standard Version of 1901, a version that uses the definite article, "the archangel", absent in the original Greek and in English translations (such as the English Standard Version of 2001, which has: "the Lord himself will descend from heaven with a cry of command, with the voice of an archangel, and with the sound of the trumpet of God").

This archangel who heralds the second coming of Christ is not named, but is probably Michael.