In verse 1 we learned how a modicum of spiritual skepticism is crucial. False spirits have gone out into the world. In my people-environment, these spirits manifest as perspectives; they come from people, devils, and even ourselves. The viewpoints of these spirits need to be tested not just accepted. In verse 2 we saw that the test is not whether they include Jesus in their religious-talk, but instead how Jesus integrates into their religious-talk. Does the person accept that Jesus was God first and man second? God from eternity come down among humanity taking on real flesh and blood?
Look now at verse 3 where John wraps up skepticism and testing.
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. (1 John 4:3–ESV)
John says every spirit that brings a different Jesus-perspective is not from God. People with such spirits may be quite sincere, genuinely interested in others, have around them kind people, strong family structures, or a myriad of other positive traits. Those are not the tests; Jesus as God come down in the flesh, that is the test.
The devil plays for keeps and is ingenious with his trickery. The frauds are already foisted: they have already gone out into the world. We must have our antennas up and tuned for truth. That way frauds will be readily detected.