The following is an excerpt from The MacArthur New Testament Commentary on 2 John 9-11.

Anyone who goes too far and does not abide in the teaching of Christ, does not have God; the one who abides in the teaching, he 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, and do not give him a greeting; for the one who gives him a greeting participates in his evil deeds. (9–11)

Those who are loyal to Scripture will naturally seek to protect and guard it. No matter what he may claim, anyone who goes too far and does not abide in the teaching of Christ does not have God. Proago (goes too far) means in this context “to go beyond established bounds of teaching or instruction, with the implication of failure to obey properly” (“proago,” Louw-Nida Greek-English Lexicon of the New Testament Based on Semantic Domains, 2nd Edition, Edited by J. P. Louw and E. A. Nida. Copyright © 1988 by the United Bible Societies, New York, NY 10023. Electronic edition, BibleWorks 7). The “established bounds of teaching or instruction” are revealed in Scripture. In 1 Corinthians 4:6 Paul wrote, “Now these things, brethren, I have figuratively applied to myself and Apollos for your sakes, so that in us you may learn not to exceed what is written, so that no one of you will become arrogant in behalf of one against the other” (emphasis added). Any teaching not consistent with Scripture is to be rejected (cf. Rev. 22:18–19).

Abide again translates the present participle of the verb meno, which means “to remain,” “continue,” or “persist in.” The teaching of Christ can refer either to His teaching, or to the biblical teaching about Him, since both are in total agreement. False teachers are not content to remain within the confines of Scripture, but invariably add erroneous interpretations, revelations, visions, words as if from the Lord, or esoteric distortions of the biblical text, while claiming to have advanced knowledge, new truth, or hidden wisdom available only to them and their followers.

But such claims are specious. John plainly states that anyone who alters, adds to, denies, or misrepresents what the Bible says about Jesus Christ does not have God (cf. Matt. 11:27; John 5:23; 15:23; 1 John 2:23; Rev. 22:18–19). Conversely, the one who abides in the teaching, he has both the Father and the Son. This is salvation language; having God and Christ must mean their indwelling presence. As Jesus declared in John 14:23, “If anyone loves Me, he will keep My word; and My Father will love him, and We will come to him and make Our abode with him.” There is no way to know God apart from faith in the Christ of Scripture (John 14:6; Acts 4:12; 1 Tim. 2:5).

In verse 10 John sets out one practical application of how to defend the truth: If anyone comes to you and does not bring this teaching, do not receive him into your house. Hospitality for traveling teachers was common in the culture (cf. Luke 9:1–6; 10:1–12). The prohibition here is not to turn away the ignorant; it does not mean that believers may not invite unbelievers—even those who belong to a cult or false religion—into their midst. That would make giving the truth to them difficult, if not impossible. The point is that believers are not to welcome and provide care for traveling false teachers, who seek to stay in their homes, thereby giving the appearance of affirming what they teach and lending them credibility.

John’s use of the conjunction ei (if) with an indicative verb indicates a condition that is likely true. Apparently, the lady to whom he wrote had for whatever reason, in the name of Christian fellowship, already welcomed false teachers into her home. It was just such compassionate, well-meaning people that the false teachers sought out (cf. 2 Tim. 3:6); since churches were supposed to be protected by elders who were skilled teachers of the Word (1 Tim. 3:2; Titus 1:9), they should have been less susceptible to the lies propagated by the deceivers. Having established themselves in homes, the false teachers hoped eventually to worm their way into the churches. It is much the same today, as false teaching insidiously invades Christian homes through television, radio, the Internet, and literature.

So threatening are these emissaries of Satan that John went on to forbid even giving them a greeting; for the one who gives him a greeting participates in his evil deeds. Irenaeus relates that the church father Polycarp, when asked by the notorious heretic Marcion, “Do you know me?” replied, “I do know you—the firstborn of Satan” (Against Heresies, 3.3.4). John himself once encountered Cerinthus (another notorious heretic) in a public bathhouse in Ephesus. Instead of greeting him, however, John turned and fled, exclaiming to those with him, “Let us fly, lest even the bath-house fall down, because Cerinthus, the enemy of the truth, is within” (Irenaeus, Against Heresies, 3.3.4).

Chairein (greeting) means “Rejoice.” It was a common Christian greeting, conveying the joy believers had in one another’s presence. But it is an affirmation of solidarity that is totally inappropriate for false teachers, who have no part in the truth or genuine Christian fellowship. Such emissaries of Satan must be exposed and shunned, not affirmed and welcomed.

False teachers like to decry such treatment as harsh, intolerant, and unloving. But love forbids allowing dangerous spiritual deception to find a foothold among Christians. John’s pastoral admonition is perfectly consistent with Jesus’ denunciation of false teachers as “ravenous wolves” (Matt. 7:15; cf. Acts 20:29); thieves and robbers (John 10:1) whose only purpose is “to steal and kill and destroy” (v. 10). The church cannot aid or abet with impunity such spiritual outlaws by doing anything that would acknowledge them as Christians. The one who does so—even by doing something as seemingly innocuous as greeting them—participates in their evil deeds by helping them further their deception.