It is no secret that Satan is powerful. In John 12:31, he is called the "prince of this world," and again in Ephesians 2:2 we see that he is the "ruler of the kingdom of the air." Since the very beginning, the Fall of Man, this world has become Satan's to do with as he pleases. For if this were God's then there would be no sin and we would be living in perfect community with Him. We would have never been made to leave the Garden of Eden. But as it is, Satan is strong and this world is his. We are living in hell on Earth.
God is holy, which means he is set apart. In him there is no sin at all, because sin is lawlessness and he has not broken the law. But we are not holy, we have broken this law, and our lives are marked with this sin. But humans are the not the only ones who have sinned; God also created angels and they too can sin. God created us to have free will, so that we would choose to worship him out of love, not out of obligation, and he has given this same authority to his heavenly host. However, "the angels who did not keep their positions of authority but abandoned their proper dwelling--these he has kept in darkness, bound with everlasting chains for judgement on the great Day"(Jude 6). And we see in Matthew 25:41 what truly become of these angels, speaking to men who do not know Jesus: "Depart from me, you who are cursed, into the eternal fire prepared for the devil and his angels."
So clearly, Satan is the ruler of the fallen angels, the king of his realms. But he was once "the seal of perfection, full of wisdom and beauty. You were in Eden, the garden of God...You were blameless in your ways from the day you were created until wickedness was found in you...Your heart became proud because of your beauty, and you corrupted your wisdom because of your splendor. So I threw you to the earth; I made a spectacle of you before kings." Satan was once the face of perfection among the angels. He was given the most power, the most beauty, the most wisdom, but this filled him with pride and he tried to take the throne of God. Satan's arrogance made him believe that he had as much power as God, even more, despite being create by God, and God shamed this angel by casting him to the earth, out of heaven, and all the angels that followed Satan with him.
And this just makes Satan furious. In his pride, he doesn't believe that he deserves this, and so he tries to show God that he has more power than God by bringing his very best creation, Man, down to the same place where he is. He tempts Adam and Eve to break the one rule that God set before them, and because of this separates us from our God. And Satan is feeling pretty good about himself right about now, he has successfully broken God's most prized possession and all men are now condemned to the same fate that he and his fallen angels now face: the pain of death in Hell.
That is why I say we are living in hell on earth, every day. God had expelled Satan from heaven by forcing him to live for eternity on this earth, and so Satan sets up shop and makes this earth his own. He convinces man to worship other gods, tells us that our lives are empty without sex, drugs, alcohol, and the approval of those who give us these things. He has us so convinced that we are too filthy to be loved by God, or that he is too far away and doesn't care, or that our very existence is mere chance, that it would take a miracle for us to believe any different. And with his host of demons there to assist him in his unholy mission, he makes sure that his presence is known here on earth more than anything else.
This is how Satan works, simply by filling man so full of himself that they can no longer see the goodness in this world. We are being tortured physically, tormented mentally, and murdered spiritually every day that we live in this world. God never intended us to live in pain, and one day we won't have to if we have faith, but for now we live in the midst of unimaginable pain standing on our doorstep. We have Satan's angels living amongst us, and sometimes even within us, literally controlling our bodies, our actions, our mouths, while our spirit has been so subdued within our own body that we ourselves literally have no control. While this is a very extreme case, we see in passages such as Mark 5, where a man is being controlled by a Legion of thousands of demons, that this is a very real thing. I have heard far too many stories, even known people who have been very strongly influenced by demons; to think that Satan isn't incredibly powerful is proof of just how powerful he is.
But while we live in a place of such darkness, with what seems like no hope, no conceivable future, Jesus shines as a light in the darkness. Because when Satan tempted Adam and Eve and God sent his judgement out on the world, he turned to the Snake and told him that he still has not won, he still hadn't taken everything from God, because one day God will send a man who "will crush your head, and you will strike his heel"(Genesis 3:15). And in Revelation 12 we see the culmination of God's power as he triumphs over the kingdom that was taken from him in the last days:
"Then war broke out 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. The great dragon was hurled down--that ancient serpent called the devil, or Satan, who leads the whole earth astray. He was hurled to the earth, and his angels with him.
Then I heard a voice in heaven say:
'Now have come the salvation and power and the kingdom of our God, and the authority of hes Messiah. For the accuser of our brothers and sisters, who accuses them before our God day and night, has been hurled down. They triumphed over him by the blood of the Lamb and the word of their testimony; they did not love their lives so much as to shrink from death. Therefore rejoice, you heavens, and you who dwell in them! But woe to the earth and the sea, because the devil has gone down to you! He is filled with fury, because he knows that his time is short.'
~ Revelation 12:7-12
So while Satan rules over this world now, we can rest assured that he is not our ultimate ruler, because he is still subject to his Creator. And by the blood Jesus poured out on the cross, we, too, triumph over sin if we have faith and put our trust in Him. Our God has won the victory, awake and sing!