The bible tells us how to spot false teachers in two ways: by what they teach and by how they live.
A few days ago, I blogged about what false teachers actually teach. They teach against the gospel. False teachers deny Christ in one way or another. On a related note, those who simply teach secondary doctrines in a way we do not like are not false teachers.
The bible instructs us that false teachers live out their false teachings. Because they teach against Christ, false teachers are not in Christ. They are not redeemed, adopted, reconciled, justified, saved, etc. False teachers are in the flesh. Because of this, false teachers will live out their lostness in worldly ways. They do not live holy lives.
Here are three scriptural examples:
Matthew 7:15-20 - "Beware of false prophets, who come to you in sheep's clothing but inwardly are ravenous wolves. You will recognize them by their fruits. Are grapes gathered from thornbushes, or figs from thistles? So, every healthy tree bears good fruit, but the diseased tree bears bad fruit. A healthy tree cannot bear bad fruit, nor can a diseased tree bear good fruit. Every tree that does not bear good fruit is cut down and thrown into the fire. Thus you will recognize them by their fruits."
II Peter 2:12-17 - "But these, like irrational animals, creatures of instinct, born to be caught and destroyed, blaspheming about matters of which they are ignorant, will also be destroyed in their destruction, suffering wrong as the wage for their wrongdoing. They count it pleasure to revel in the daytime. They are blots and blemishes, reveling in their deceptions,while they feast with you. They have eyes full of adultery, insatiable for sin. They entice unsteady souls. They have hearts trained in greed. Accursed children! Forsaking the right way, they have gone astray. They have followed the way of Balaam, the son of Beor, who loved gain from wrongdoing,but was rebuked for his own transgression; a speechless donkey spoke with human voice and restrained the prophet's madness. These are waterless springs and mists driven by a storm. For them the gloom of utter darkness has been reserved."
Jude 4, 8, 16, 18-19 - "For certain people have crept in unnoticed who long ago were designated for this condemnation, ungodly people, who pervert the grace of our God into sensuality and deny our only Master and Lord, Jesus Christ...Yet in like manner these people also, relying on their dreams, defile the flesh, reject authority, and blaspheme the glorious ones...These are grumblers, malcontents, following their own sinful desires; they are loud-mouthed boasters, showing favoritism to gain advantage...They said to you, 'In the last time there will be scoffers, following their own ungodly passions.' It is these who cause divisions, worldly people, devoid of the Spirit."
When we think of false teachers, we mainly think about the content of what they say. However, these passages make it clear that we should also be looking at their behavior. We can spot them through their fleshly, sensual, worldly actions. They cannot help but live this way because they do not know Christ. While claiming to teach for God and about God, they instead remain dead in their sins and under God's wrath.
We must be careful to protect the church from false teachers. We must be on guard against false teachers from both outside and inside the church. Acts 20:29-30, "I know that after my departure fierce wolves will come in among you, not sparing the flock; and from among your own selves will arise men speaking twisted things, to draw away the disciples after them."
What do we do when we spot false teaching? Our duty is to humbly speak the truth in love. Although somewhat out of context, I believe we must follow Ephesians 4:15, "Rather, speaking the truth in love, we are to grow up in every way into him who is the head, into Christ."
The goal in confronting a false teacher should not be victory in an argument. Rather, the goal should be the salvation of that false teacher.