Many deceivers have gone out into the world, those who do not confess that Jesus Christ has come in the flesh; any such person is the deceiver and the antichrist!
Be on your guard, so that you do not lose what we have worked for, but may receive a full reward.
References for 2 John 1:8
Everyone who does not abide in the teaching of Christ, but goes beyond it, does not have God; whoever abides in the teaching has both the Father and the Son.
Do not receive into the house or welcome anyone who comes to you and does not bring this teaching;
for to welcome is to participate in the evil deeds of such a person.
Although I have much to write to you, I would rather not use paper and ink; instead I hope to come to you and talk with you face to face, so that our joy may be complete.
The children of your elect sister send you their greetings.
References for 2 John 1:13