2 John 1:6-9

And this is love: that we walk in accordance with His commandments and are guided continually by His precepts. This is the commandment, just as you have heard from the beginning, that you should [always] walk in love. 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]. Anyone who runs on ahead and does not remain in the doctrine of Christ [that is, one who is not content with what He taught], does not have God; but the one who continues to remain in the teaching [of Christ does have God], he has both the Father and the Son.