2 Peter 2:1-3
But false prophets arose among the people, just as there will be false teachers among you. These false teachers will infiltrate your midst with destructive heresies, even to the point of denying the Master who bought them. As a result, they will bring swift destruction on themselves. And many will follow their debauched lifestyles. Because of these false teachers, the way of truth will be slandered. And in their greed they will exploit you with deceptive words. Their condemnation pronounced long ago is not sitting idly by; their destruction is not asleep.
If false teachers were not dangerous, we would not be warned about them in scripture. If anyone teaches denying or rejecting Jesus Christ, they are a false teacher. 1 John 4:1-3 (NIV) says, “Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world. This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God, but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world.” The Holy Spirit lives within us as believers in Christ Jesus, and He is trustworthy. Partner with Him to test the integrity of what is being taught, and to protect from being led astray.