Expositor's Bible Commentary Commentary 1 John 4:3

"and every spirit that confesseth not Jesus is not of God: and this is the [spirit] of the antichrist, whereof ye have heard that it cometh; and now it is in the world already." — 1 John 4:3 (ASV)

Here a negative confession gives the counterpart of that in v.2, and the source of this denial is seen as “the spirit of the antichrist.” John reminds his followers that Jesus had warned that the Antichrist would come. It is now John’s painful duty to announce that in the false teachers (cf. 2:18ff.) the spirit of antichrist is already present. By this the community was warned that the conflict between the false teachers and John was not a “leadership” or “personality” one. The Gospel itself was at stake. The struggle they were facing was not against flesh and blood but against principalities and powers (Ephesians 6:12). Hence, whatever success the opponents had had within the community resulted from satanic inspiration.