A.T. Robertson Commentary 1 John 4:1

"Beloved, believe not every spirit, but prove the spirits, whether they are of God; because many false prophets are gone out into the world." — 1 John 4:1 (ASV)

Beloved (αγαπητο). Three times in this chapter (1,7,11) we have this tender address on love.

Believe not every spirit (μη παντ πνευματ πιστευετε). "Stop believing," as some were clearly carried away by the spirits of error rampant among them, both Docetic and Cerinthian Gnostics. Credulity means gullibility and some believers fall easy victims to the latest fads in spiritualistic humbuggery.

Prove the spirits (δοκιμαζετε τα πνευματα). Put them to the acid test of truth as the metallurgist does his metals. If it stands the test like a coin, it is acceptable (δοκιμος, 2 Corinthians 10:18), otherwise it is rejected (αδοκιμος, 1 Corinthians 9:27; 2 Corinthians 13:5–7).

Many false prophets (πολλο ψευδοπροφητα). Jesus had warned people against them (Matthew 7:15), even when they as false Christs work portents (Matthew 24:11,24). It is an old story (Luke 6:26) and recurs again and again (Acts 13:6; Revelation 16:13; Revelation 19:20; Revelation 20:10) along with false teachers (2 Peter 2:1).

Are gone out (εξεληλυθασιν). Perfect active indicative of εξερχομα. Cf. aorist in 2:19. They are abroad always.