1 John 4:2-3
2 By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God, 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.
We live in a world in which religious tolerance is at a premium. Why can’t we all just get along? Why can’t we see that we all worship the same God? The answer to that last question is easy: We don’t worship the same God. We can’t get along because, fundamentally, people of differing world religions disagree about the central point of who God is.
John, in writing 1 John, did not have a problem spelling out the reason for the trouble and conflict between different religions. It came down to one simple question. Do those who believe a certain religion acknowledge Jesus? This, of course, is more than saying that a man named Jesus lived years ago. The question was a question of the nature of Jesus. Do you recognize Jesus as fully God and fully man? If you deny both the deity and humanity of Jesus, you cannot be Christian.
IN fact, look at John’s words. When speaking of those who deny the fundamental nature of Jesus, John speaks pretty harshly. Those who deny that Jesus has come in the flesh are antichrist. To miss the identity of Jesus is to miss God. To lower Jesus to mere humanity is to blaspheme God. To miss the fact that Jesus did become human is to deny key elements of the atoning work of Jesus. Simply put, if you want your religion to be the religion of God, you had better get the person of Christ right
There are lots of ways in which people in the world ought to be tolerant. We should be kind to those who see the world differently than we do. However, if someone denies the identity of Jesus, we cannot call them in any way people of God. God’s word says that to deny Jesus is antichrist, and that is a very serious thing.