And by this we know that he abides in us, by the Spirit whom he has given us. Beloved, do not believe every spirit, but test the spirits to see whether they are from God, for many false prophets have gone out into the world. By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God, 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. Little children, you are from God and have overcome them, for he who is in you is greater than he who is in the world. They are from the world; therefore they speak from the world, and the world listens to them. We are from God. Whoever knows God listens to us; whoever is not from God does not listen to us. By this we know the Spirit of truth and the spirit of error. (1 John 3:24b-4:6)
When we become Christians, through faith and baptism, we are given God's Holy Spirit as a gift. There are no exceptions. There's no delay. Just as we are washed clean with Christ's blood from all sin, so, too, we are given a down-payment of the Holy Spirit as a promise of everlasting life. Now, God's Spirit does not lie dormant in us, but he performs certain functions while we still live on earth. One of these is testing the spirits.
There are other spirits than the Holy Spirit, angels and demons, and according to our passage in 1 John, we are to test them to see if they are from God or not. These spirits interact in our world behind the scenes, influencing things, either on God's behalf or against God. Since the Holy Spirit is perfectly good and holy, he will never lead us astray. Just as he interprets the scriptures for us, he also discerns the spirits that are in the world. This doesn't mean that we suddenly see angels and demons wandering around. No, we see the influence the Spirits have on people, and it's through observing and listening to the people--what they do and what they say--that we can see the influence the spirits have.
So, when pastors who are supposed to be teaching the truth about God from the scriptures, instead preach themselves or come up with false doctrine for shameful gain, leading their congregations astray, those who have the Holy Spirit will be able to detect this, and depart from under the false teacher's influence. These "false prophets," as John calls them, have false spirits influencing them. The Holy Spirit detects and rejects these false spirits.
Now, John gives us the test. This is how it looks to us. It seems as if we are just using logic, and the test is a logical one, but without the Spirit, we are easily fooled, and the false things we hear are easily digestible, easily incorporated into our worldview, and we are led further and further astray from God.
Here's the test: the Spirit that confesses that Jesus Christ has come in the flesh is from God. That seems pretty straightforward doesn't it? In fact it seems so simple, why wouldn't anyone say that this statement is true? However, there are many truths loaded in that one statement. So what does "Jesus Christ has come in the flesh" mean?
First, Jesus was the Christ, the messiah, the anointed one, the savior of mankind. The Old Testament promises a messiah who will save God's people from all their sins. Jesus is that messiah.
Second, Jesus was fully God. The scriptures say that the messiah is going to be God himself. So, Jesus, in being the Christ, is fully divine with all the powers and attributes of God.
Third, Jesus was fully human. This is what is loaded inside the clause, "in the flesh." Jesus lived as a man. He bled, he died, he showed emotion, he wept, he touched things and interacted with other humans on a real level.
Fourth, the incarnation really happened. This is important. Ancient heresies that are still around today claim that since Jesus was God, he just appeared to be a man. Or Jesus was just a man, a great moral teacher, who wasn't really God but had the divine spark in him. No, Jesus is God, and as the second part of the trinity, he was incarnate on earth, born of a virgin, and lived out a fully human life on earth, but at the same time he was fully God. He died like a man, but he rose again from the dead by the will of God.
Fifth, he taught as a man but with divine authority. His teachings are pure and good, because he does not lie. He always backed up his teaching with miracles that only could happen from God, including instantly healing the sick and raising the dead. We believe his teachings as true because he was God. We follow his teachings because he was fully man, who could lead by example.
Sixth, he did not sin. Being fully God, he was purely good and was incapable of sin. Being fully man, he was tempted by the evil spirits, just as we are. As God, he resisted the temptations and remained sin-free. As man, his sacrifice on the cross enables his perfect righteousness to be imputed to us and our actual sins to be imputed to him. A God who only appeared to be man is not capable of being a human sacrifice for our sins.
Seventh, he actually died. Being in the flesh, he was actually able to die. He was tortured, beaten--he bled. He was hung on a cross, suffocated--he died a true death. Being fully God he was able to take on himself the sins of the world. Being fully man, he was able to be killed in our place. If he did not die in our place, we are doomed and must suffer eternal death ourselves.
Eighth, he rose from the grave into a new body of flesh. As Christians, our goal is to attain the resurrection from the dead to eternal life. Jesus showed us what this looks like. His resurrection body is flesh, indestructible flesh, and so we are not to anticipate a spiritual-only resurrection. Many Gnostic heresies speak only of a spiritual resurrection, the flesh being bad, and so many false teachings come with that idea. If flesh is bad, then why would our good God create anything inherently bad? Suddenly our God stops being the creator God who made heaven and earth. The new heavens and the new earth aren't going to be spiritual places but actual places that we can experience with our senses. Christ's resurrection is the first fruit of that reality.
Without these eight details we have no hope. We are most to be pitied, because we are putting our trust in an illusion. Without Jesus Christ having come in the flesh, was are still dead in our trespasses and have to account for our sins on the day of judgment. Without Christ in the flesh, we are ruined.
And the false spirits are still active in the world today. The false teachings are still happening. Many, many sermons and teachings about Christ are not really about Jesus Christ but about us, our lives here and now, and how Jesus can magically help us through our earthly problems. Jesus' name becomes a magical code word that allows God access to our selfish, sinful lives. God becomes a comforter and helper without being our savior. Jesus becomes a genie who can give us prosperity and riches and fame. When a teacher is avoiding the cross, because the cross itself implies an actual death of an actual man, when a teacher avoids talking about that, he reveals himself as one who does not believe that Jesus Christ has come in the flesh. He may believe in one aspect of Jesus' nature or the other--perhaps fully God, perhaps fully man--but there is a false spirit with that teacher who is keeping the two natures of Christ apart.
All the cults preach a Christ who was not God but only a man, maybe a man with the divine spark but a man nonetheless. Those teachers are easier to discern because the whole point of Christianity is that we believe that Jesus was God. However, more subtle is the preaching that Jesus was God but that his humanity is irrelevant. Remember, salvation is impossible without Christ being fully man as well as fully God. Preaching and teaching that focuses on ourselves and Jesus as our genie, or a mystical, personal experience with a spiritual Christ, is preaching that denies his humanity.
Of course, that is why we have the Holy Spirit. Even though the phrase is simple and logical--Jesus Christ has come in the flesh--the devil has created many ways for us to be deceived from this simple truth. Without the Spirit in us, even this test becomes impossible to perform, because the false spirits are tricky and will tempt us to believe in anything, just as it was tempting these Christians, to whom John was writing, to doubt Christ come in the flesh.
That is why John begins this very letter with the following: That which was from the beginning, which we have heard, which we have seen with our eyes, which we looked upon and have touched with our hands, concerning the word of life—the life was made manifest, and we have seen it, and testify to it and proclaim to you the eternal life, which was with the Father and was made manifest to us—that which we have seen and heard we proclaim also to you, so that you too may have fellowship with us; and indeed our fellowship is with the Father and with his Son Jesus Christ. And we are writing these things so that our joy may be complete.
See how many times John describes experiencing Jesus Christ with his human senses. Christ come in the flesh is of paramount importance to our salvation. Thankfully, God has given us his Holy Spirit to reveal this truth to us and to test the spirits to discern the truth in others who proclaim Jesus. Remember, he who is in you is greater than he who is in the world.