Know Your Enemy!
Revelation 12:19 lists a few names of the angel who rebelled against God in Heaven; the dragon, the devil, Satan, and that ancient serpent. Revelation 12:8 shows that at one time Satan had a place in Heaven, but no longer. He was thrown down to earth, but not only him, but other angels as well. Revelation 12:4 indicates that in Satan's rebellion he brought 1/3 of the angels of Heaven with him - so 1/3 of the angels believed the lie of the dragon, the ancient serpent - they were promised something Satan couldn't deliver. Satan's rebellion resulted in war in Heaven. Michael and his angels went to war against the dragon and his angels. When Satan was thrown down to earth he was allowed to "operate", he was allowed to do things, he was given certain authority. What he does, who he is, is told in verse nine, "he is deceiver of the whole world". Verse 12 says, he has come down to earth with great wrath. Verse 17 tell us the dragon makes war with the Saints, the Believers, the followers of Christ. Lest a person think of Satan is one without ability, or authority, consider this, verse 10 shows us Satan's access to God, access and authority to accuse the brethren to God- but he doesn't just occasionally bring accusation, he accuses them day and night.
So consider this; an angel so magnificent and powerful that he thought he could overthrow God, the Creator of all things, the One who created him; not only that, but, his ability to deceive is so grand that he has was able to convince 1/3 of the angels to go along with the rebellion; this is your enemy. Satan and his angels have been given authority to deceive and make war against the brethren and they are carrying out this mission with great wrath and fury. In addition, he has been given access to God to accuse the brethren day and night. If that is not enough, he is able to give his power, his throne, and his great authority to whomever he wishes, and he will do that for the beast, who will likely already have great power and influence in the world.
THIS IS YOUR ENEMY!