Submit yourselves therefore to God. Resist the devil, and he will flee from you. Draw near to God, and he will draw near to you. Cleanse your hands, you sinners, and purify your hearts, you double-minded.
In this passage we see the Lord and the Devil moving in two different directions. The Devil is fleeing and and Lord is drawing near. This explains why the Devil flees, because God is coming!
We see all the Devil is doing in this world, and what he has done in our own lives, and he can be pretty scary. He is described in Scripture as the adversary, the prince of the power of the darkness, the enemy, the accuser of our brethren, a dragon, a serpent, a lion, the god of this age, the evil one, the father of lies, a murderer, the tempter, and the ruler of this world (Matthew 4:3; 13:38-39; John 8:44; 12:31; 2 Corinthians 4:4; Ephesians 2:2; 1 Peter 5:8; Revelation 12:9-10).
When I think of a lion, a ruler, a god, and a dragon, the thought of those beings fleeing anything is foreign to me. But when the Lord is coming, that great dragon and roaring lion runs away! The Devil is powerful, he has brought the whole world under his influence (1 John 5:19), but He who is in us is greater than he who is in the world (1 John 4:4).
If you submit to God, resist the devil, and draw near to God, the Lord promised two things: He would come near, and the Devil would run away. That’s a promise. God doesn’t lie. Sometimes we get too caught up in the power of the Devil and forget how much more mighty the Lord Jesus is.
He who sins is of the devil, for the devil has sinned from the beginning. For this purpose the Son of God was manifested, that He might destroy the works of the devil.
(1 John 3:8)