For many deceivers [heretics, posing as Christians] have gone out into the world, those who do not acknowledge and confess the coming of Jesus Christ in the flesh (bodily form). This [person, the kind who does this] is the deceiver and the antichrist [that is, the antagonist of Christ].

Watch yourselves, so that you do not lose what we have accomplished together, but that you may receive a full and perfect reward [when He grants rewards to faithful believers].

for the one who gives him a greeting [who encourages him or wishes him success, unwittingly] participates in his evil deeds.