1 John 4:4-6
4 You, dear children, are from God and have overcome them, because the one who is in you is greater than the one who is in the world. 5 They are from the world and therefore speak from the viewpoint of the world, and the world listens to them. 6 We are from God, and whoever knows God listens to us; but whoever is not from God does not listen to us. This is how we recognize the Spirit of truth and the spirit of falsehood.
After warning of the dangers of these false teachers, John encourages the believers with these words. First, he says they have overcome them. Though we are tempted in this life through bad teaching and behavior, the battle is over. And then he gives us an amazing promise when he says, "Greater is he that is in you, than he that is in the world." Of course he is referring to the Holy Spirit, who is in you when you come to faith. He that is in the world is Satan, or the devil, who works overtime through these false teachers to confuse and deceive believers. That is his main goal.
But even though we need to be aware of the devil and his schemes (2 Corinthians 2:11), we don't need to be afraid of him. Why? Because the One who lives in you is the greater than the one who is in the world. We have the power of Jesus, and the power of His resurrection living in us. We have the authority to rebuke the devil and he will flee from us. Paul says this about Jesus' work on the cross, "And having disarmed the powers and authorities, he made a public spectacle of them, triumphing over them by the cross." (Colossians 2:15)
So again John is looking at his dear children, his sons and daughters in the faith, and saying, "Although need to be aware of these false teachers who are trying to corrupt you, you don't need to be afraid of them." If you are in Him, you have the Spirit who will help you to discern false teachers.
Where are you vulnerable to false teaching? What teaching from the world is most likely to tempt you as a believer? God has given us His Word and His Spirit to continue to guide us in the Truth and warn us of error. This is a greater power than anything of or in the world can touch!