For many deceivers have gone out into the world, those who do not confess the coming of Jesus Christ in the flesh. Such a one is the deceiver and the antichrist. Watch yourselves, so that you may not lose what we have worked for, but may win a full reward. Everyone who goes on ahead and does not abide in the teaching of Christ, does not have God. Whoever abides in the teaching has both the Father and the Son. If anyone comes to you and does not bring this teaching, do not receive him into your house or give him any greeting, for whoever greets him takes part in his wicked works. (2 John 1:7-11 ESV)
The context of this passage clearly refers to traveling teachers or preachers working against true Christian teaching. Do not receive them into your house. Such a welcome would give the appearance of endorsing the false teaching. This is not a prohibition about showing the hospitality to sinners for which Yeshua was well known and criticized (Matthew 9:10–13; 11:19).
The Apostle Paul also warned against overzealous separation from non-believers. “I wrote to you in my letter not to associate with sexually immoral people — not at all meaning the sexually immoral of this world, or the greedy and swindlers, or idolaters, since then you would need to go out of the world” (1 Corinthians 5:9-10 ESV).
It is rather false Christians (cults and apostate groups) that require caution and perhaps rejection. “But now I am writing to you not to associate with anyone who bears the name of brother if he is guilty of sexual immorality or greed, or is an idolater, reviler, drunkard, or swindler–not even to eat with such a one. For what have I to do with judging outsiders? Is it not those inside the church whom you are to judge? God judges those outside. “Purge the evil person from among you”” (1 Corinthians 5:11-13 ESV).
The significance of the Apostle John’s call to reject any false teacher was heightened in a society that considered hospitality a great virtue. Hospitality, much admired in both Greco-Roman and Jewish sources (1 Timothy 3:2; Titus 1:8), was much needed in an era when inns could be dangerous and unpleasant.
To greet such a person meant to extend approval, assistance, and full fellowship. To support someone who is working against the true Christian message makes those supporting them liable for that person’s guilt.
The gospel is unchanging. Therefore, the Apostle Paul pronounces a curse of final judgment on those who proclaim or receive a different gospel. Even if one of the Apostles or an angel from heaven were to preach such a gospel, believers should reject it. Mormonism, Islam and Jehovah’s Witnesses are examples of religions that are based on revelation supposedly given by an angel and that teaches a gospel different from justification by faith alone in the substitutionary death of Yeshua.
I am astonished that you are so quickly deserting him who called you in the grace of Christ and are turning to a different gospel — not that there is another one, but there are some who trouble you and want to distort the gospel of Christ. But even if we or an angel from heaven should preach to you a gospel contrary to the one we preached to you, let him be accursed. As we have said before, so now I say again: If anyone is preaching to you a gospel contrary to the one you received, let him be accursed.
(Galatians 1:6-9 ESV)