John wrote, "Stop believing." Evidently some of his first readers where believing false teaching. [source][source][source]
"Credulity means gullibility and some believers fall easy victims to the latest fads in spiritualistic humbuggery." [1][source]
It is necessary to distinguish the Spirit of God from false spirits (i.e, spirits advocating falsehood) because many false prophets have gone out into the world. False spirits (utterances or persons inspired by a spirit opposed to Christ) produce false teaching. [source][source][source]
"To "test the spirits" is to make a choice from among competing claims." [2][source]
John"s test question whereby one can determine whether the Spirit of God or a spirit of falsehood possesses a person was this. What does the person believe about Jesus Christ? If a person denies the incarnation of Jesus Christ-a heresy false teachers were promoting among John"s original readers-he has the spirit of antichrist (cf. 1 John 2:18-27). That Isaiah , a denial of the doctrine of Christ as the apostles taught it, deviation from orthodox Christology, evidences a spirit opposed to Jesus Christ. [source][source][source]
"The test of the presence of the Divine Spirit is the confession of the Incarnation, or, more exactly, of the Incarnate Saviour. The Gospel centres in a Person and not in any truth, even the greatest, about the Person." [3][source]
Notice that John did not say we can tell false spirits by their works. He said we can identify that they are false spirits by their message. This was the acid test of a false prophet under the Old Covenant as well ( Deuteronomy 13:1-5). [source][source][source]
"According to the Lord Jesus, false prophets were to be tested "by their fruits" (cf. Matthew 7:16-20). Contrary to popular interpretation, this does not mean that they were to be tested by their works. On the contrary, as Matthew 12:33-37 proves, their fruits are their words! Indeed, as the Lord Himself said, they "come to you in sheep"s clothing" so that they look like sheep when in reality they are "ravenous wolves" ( Matthew 7:15). Their behavior does not set them apart from the sheep, but their message does!" [4][source]
John did not say that every spirit that denies Jesus, but every spirit that does not confess Jesus ( 1 John 4:3). Often heretical teaching masks its deviations from the truth by simply failing to affirm important biblical truth. Rather than proclaiming, "Jesus is not the Christ," they fail to affirm that He is the Christ. [source][source][source]