Revelation 12:7-9 tells the story of the war in heaven:
Then war broke out in heaven; Michael and his angels battled against the dragon. The dragon and its angels fought back, but they did not prevail and there was no longer any place for them in heaven.
The huge dragon, the ancient serpent, who is called the Devil and Satan, who deceived the whole world, was thrown down to earth, and its angels were thrown down with it.
These verses come right after the Woman Clothed with the Sun gives birth and flees into the desert where she had a place prepared by God. We understand that to refer to the Virgin Birth, while the war in heaven occurred, we are told, when the devil and its angels first fell.
Maybe we can say the devil underwent a series of falls, with the logical progression more important than the chronology. First is the fall from grace, when the devil first opposed God's will, which parallels Adam's fall in eating the forbidden fruit.
Next is the fall from heaven, moved along by Michael and his angels. It parallels Adam's expulsion from Paradise, though it may not have been quite as complete. Instead of being kept out by an angel with a flaming sword, Satan is able to come before the LORD.
After the Incarnation, though -- and again, "after" in the logical sense, not necessarily the chronological sense -- there was no longer any place for the devil and its angels in heaven. God's will had triumphed; God's plan had been carried out, despite the worst the devil could do. At this point, the New Adam beats a separate path back to God, and mankind is no longer doomed to follow the devil on its downward journey.
Revelation 12 continues:
Then I heard a loud voice in heaven say: "Now have salvation and power come, and the kingdom of our God and the authority of his Anointed. For the accuser of our brothers is cast out, who accuses them before our God day and night. They conquered him by the blood of the Lamb and by the word of their testimony; love for life did not deter them from death."
Michael, the Incarnation, Christian martyrs -- who or what doesn't cast down the devil? But you see how this passage identifies Michael's victory with the martyrs'. Michael throws the devil down to earth, and the martyrs overcome it by Christ. In both cases, the devil works to foil God's will, and is defeated by those who work to keep it.
The loud voice continues:
"Therefore, rejoice, you heavens, and you who dwell in them. But woe to you, earth and sea, for the Devil has come down to you in great fury, for he knows he has but a short time."
Here's the downer, for those of us who happen to dwell on the earth and sea. Cast out of heaven, and faced with an eternity in hell, the devil is tearing it up right here.
That's regrettable, but it's the sort of thing you'd want to know about where you dwell. And recall: there is no longer any place for the devil and its angels in heaven.
So if the devil is mad as hell here on earth, and has already been cast out of heaven, then the thing to do is...?
Right! Conquered him by the blood of the Lamb and by the word of your testimony. To that extent, you will already be in heaven even as you dwell on earth. To that extent, you may rejoice!