The Remnant is what is left when the majority is gone. In the Bible the Remnant are the few faithful individuals out of the majority who have turned away from God. In the Last Days the Remnant will keep the Commandments of God and have the Testimony of Jesus.
A comparison of many scriptures shows that Michael the Archangel is actually the Lord Jesus Christ in His role of opposing Satan and rebuking his claims. As Michael Jesus cast Satan out of Heaven and will eventually cast him into the Lake of Fire where he will be destroyed.
Revelation 12 describes War in Heaven in which Satan, the “Dragon”, is cast out of Heaven. This is actually a continuation of the Great Controversy which began when Satan challenged God and accused Him of being unjust. Sin entered this world when Adam and Eve accepted Satan’s accusations.