1 John 4:3
 and every spirit that does not confess Jesus is not from God. This is the spirit of the antichrist, which you heard was coming and now is in the world already. (ESV)
What does it mean to "confess Jesus?" Let's look at that idea together. This concept can be defined as "genuinely proclaiming the truth about Jesus' true nature." John has just established that the truth about Jesus involves both his eternal deity as well as his coming in human flesh. Those who deny those truths and confess a Jesus that is different are not from God.
It is important to know that many will claim to confess Jesus, yet we are not to be fooled. We are to test the spirits to see if they truly speak from the inspiration and leading of God's Holy Spirit. If they do not pass that test then we know that they are led by a different spirit. That spirit is now here defined as the spirit of the antichrist.
In our world that wants to accept every person and every teaching it is hard to deal with this idea that those who teach different truths about Jesus are led by a spirit of antichrist. We struggle to make the hard distinctions between our Biblical faith and the faith that is held by those of other religions. We do not seem to like the exclusive nature of our faith. Yet, Jesus himself proclaimed a very exclusive truth.
 Whoever is not with me is against me, and whoever does not gather with me scatters. (ESV)
 Jesus said to him, “I am the way, and the truth, and the life. No one comes to the Father except through me. (ESV)
Do you confess Jesus? Do you agree with the truth claims that he has given? Or are you enticed by a spirit of antichrist? His truth is exclusive, but it is the only way to eternal life.