1 John 4:1-6
Beloved, do not believe every spirit, but test the spirits, whether they are of God; because many false prophets have gone out into the world.

John encourages us to “test” the spirits of those who claim to speak for God, because there are many who are false.

By this you know the spirit of God: Every spirit that confesses that Jesus Christ has come in the flesh is of God, and every spirit that does not confess that Jesus Christ has come in the flesh is not of God. And this is the spirit of antichrist, which you have heard was coming, and is now already in the world.

John says we can know these false teachers by their confession that Jesus Christ has come in the flesh. Do you think their ability to say these words proved that they were of God? I think not. He meant more than confessing with words. Other scriptures (Matthew 7:21-27) confirm that words alone are not enough. Could he mean that we can know them because their Godly life confesses that Jesus has come in their flesh – that He lives in them. And likewise, we can know by their ungodly life that Jesus has not come in their flesh and that they are not of God. Furthermore John says that this ungodly lifestyle of those who claimed to speak for God is the spirit of antichrist which was already in the world.

You are of God, little children, and have overcome them, because He who is in you is greater than he who is in the world. They are of the world. Therefore they speak as of the world, and the world hears them.

Since they were of God, He who was in them – in their flesh, was greater than the worldly Spirit of antichrist. These teachers who lived worldly lives and spoke of the world were received by the world – not by the true Christians. Consider what John said in 1 John 2:15-17,Do not love the world or the things in the world. If anyone loves the world, the love of the Father is not in him. For all that is in the world – the lust of the flesh, the lust of the eyes, and the pride of life – is not of the Father but is of the world. And the world is passing away, and the lust of it; but he who does the will of God abides for ever.

He who knows God hears us; he who is not of God does not hear us. By this we know the spirit of truth and the spirit of error.

John was confident that a true Christian would receive the instruction – that a true messenger of God must live a life that shows that Christ is in him.

Some related passages:

Revelation 2:2:

The church at Ephesus had tested those who said they were apostles and were not.

Matthew 7:15-26:

Jesus said we could know false prophets – wolves in sheep’s clothing – by their fruits, just as we would know a tree by it’s fruit.

1 Timothy 6:3-5:

Paul taught that if a man’s doctrine didn’t teach godliness, the man was destitute of the truth. He also taught that we should get away from those who teach that gain is godliness.