Michael is not Christ. He is the spirit being, "the great prince" (Daniel 12:1), sent to serve Israel. Michael and the other princes over the nations (see Daniel 8:15-16; 9:20-23; 10:10-14, 20-21) are all subject to Christ, who is Supreme Ruler under the Father.
The chief princes among God's created spirit beings have great power and authority over the nations. But what is the limit of their authority? How far does their authority and power extend? Notice Jude 8-9: ". . . these dreamers [ungodly men] defile the flesh, reject authority, and speak evil of dignities. Yet Michael the archangel, in contending with the devil, when he disputed about the body of Moses, dared not bring against him a reviling accusation, but said, 'The Lord [Christ, who is Michael's superior] rebuke you!'"
While evil men have little or no respect for those in authority, Michael, who is an angel of the highest order, showed respect to the office of authority even of Satan the Devil! By this scripture, we can see clearly that Michael does not have greater rank than Satan. If he did, he would have given the Devil a command; he could have done the rebuking himself, instead of saying, "The Lord rebuke you!"
Christ, however, does have greater rank. Matthew 4:10 records His sharp, authoritative command to the Devil: "Away with you, Satan!" He has authority over him because He created him as the cherub Lucifer (Isaiah 14:12; Ezekiel 28:15). Christ is the One through whom the Father created all things (Colossians 1:15-16; John 1:1-3).
It is obvious that Michael could not have been Christ. Rather, he is an angelic being who is in authority over other lesser angelic beings in God's government (Revelation 12:7). He is shown in Scripture to be a leader of heavenly forces always poised to combat Satan and his demons on behalf of God's people.
Additional Scriptures: Luke 1:19, 26