John commanded his readers to “test the spirits” in order to avoid a teacher who is not speaking from the spirit of God. He then focuses on those who are speaking from a different spirit, false teachers. This refers to those who left John’s churches, those who have already been called antichrist and sons of the devil. How is it that these people can speak God’s word in the Spirit?
It is quite possible these people are not actually Christians and are under the inspiration of demonic forces to appear to be from God, or they are faking the ecstatic speech in order to give their teaching the appearance of spiritual authority. They may not even be aware their activity is false; ecstatic speech can be learned and a person could be fooling themselves into thinking their speech is from God.
It is also possible the opponents are well-meaning Christians who are genuinely trying to teach accurately about Jesus, but they sincerely disagree with John about who Jesus was. In the Gospels themselves it is clear even the disciples were not exactly clear on who Jesus was or what he came to do. When Peter finally confesses Jesus as messiah, Jesus tells Peter the purpose of the messiah is to go to Jerusalem to suffer and die. Peter rebukes Jesus since this is not what he expected messiah to do! When the false prophets “go out into the world” they have demonstrated their rebellion from God. In John’s Gospel the world is a place of darkness and it is the domain of Satan.
There are many warnings to not believe every teacher who claims to be teaching the truth about Jesus in the New Testament. In the Sermon on the Mount, Jesus says not everyone who says “Lord, Lord” will enter into the Kingdom of God (Matt 7:21-23). These people will claim to have prophesied in the name of Jesus, cast out demons and other miracles in the name of Jesus. Jesus says he will “tell them plainly, ‘I never knew you.’”
In the Olivet Discourse Jesus says many false prophets will compete with the Gospel until he returns to establish his kingdom (Matt 24:22). In Matthew 24:24, the false messiahs will do “great signs and wonders in order to deceive.” In the final three parables in Matthew 25 there are a series of people who think they ought to be in the kingdom at the time of the final judgment yet are left on the outside, in the darkness where there is weeping and gnashing of teeth. In 25:11, the foolish virgins say “Lord, Lord” yet remain in the darkness; in 25:30 the foolish servant is cast out into the darkness, and the ones who failed to help “the least of these brothers of mine” will be sent off to the hell prepared for the devil and his angels (25:41; 46).
Paul warns the Corinthian church about “false apostles, deceitful workmen, disguising themselves as apostles of Christ” (2 Cor 11:13-14). He draws a parallel to Satan who disguises himself as an angel of light. Although Paul does not specifically mention it 2 Corinthians, it is quite likely these “super apostles” did the same kinds of signs which accompanied the Twelve Apostles in order to authenticate their message. In fact, Paul included “lying signs and wonders” in his description of the coming man of lawlessness in 2 Thessalonians 2.
The book of Revelation has much to say about deceptive signs and wonders. The Lord comments the church at Ephesus for testing the who call themselves apostles and are not, and found them to be false” (2:2). This is important since 1 John was written to the churches in Ephesus at the same time Revelation was written. In the church at Thyatira there was a false teacher John calls Jezebel who calls herself a prophetess and deceives people (2:20). During the tribulation period itself the false prophet will do great signs which will deceive the people of the earth and convince them to worship the image of the beast (13:11-15).
John is therefore consistent with the rest of the New Testament when he tells his congregation to “test the spirits” by not believing everyone who claims to be a Spirit inspired prophet. In this context he gives only criterion for testing a teacher, “what do they confess about Jesus?”