For he that biddeth him God speed, is partaker of his evil deeds - Shows that he countenances and approves of the doctrine which is taught. Compare the notes at 1-Timothy 5:22.

Is partaker of his evil deeds - He that acts towards him as if he considered him a Christian brother, and sound in the faith, puts it in his power to deceive others, by thus apparently accrediting his ministry. No sound Christian should countenance any man as a Gospel minister, who holds and preaches erroneous doctrines; especially concerning the Lord Jesus. Nor can any Christian attend the ministry of such teachers without being criminal in the sight of God. He who attends their ministry is, in effect, bidding them God speed; no matter whether such belong to an established Church, or to any congregation of dissenters from it. But what St. John says here does not mean that we should deny such the common offices of humanity, charity, and mercy. No. In these offices we are equally bound to all men; far less does it intimate that we should persecute such on account of their heretical or heterodox sentiments. No. This right has God given to no man, to no Church, to no state. They who persecute others, even for the worst heretical opinions, may expect the heaviest judgments of Almighty God.
There is a remarkable addition here in several MSS. Of the Vulgate, and in some printed editions. Ecce praedixi vobis, ut in diem Domini nostri Jesu Christi non confundamini. "Behold, I have foretold this to you, that ye may not be confounded in the day of our Lord Jesus Christ."
This addition is found in the edition of Pope Sixtus the Fifth, and in the Complutensian Polyglot; but it is not acknowledged by any of the versions, nor by any Greek MSS.

For he that biddeth him God speed,.... Wishes him well, and success in his ministry, or in a friendly and familiar way converses with him:
is partaker of his evil deeds; he has fellowship with him, instead of reproving or shunning him, as he ought; he is an abettor of him in his principles, and so far joins in the propagation of them, and helps to spread them, and gives too much reason to think he is one with him in them.

By wishing a false brother or teacher "God (or 'good') speed," you imply that he is capable as such of good speed and joy (the literal meaning of the Greek), and that you wish him it while opposing Christ; so you identify yourself with "his evil deeds." The Greek of "partaker" is "having communion with." We cannot have communion with saints and with Antichrist at the same time. Here we see John's naturally fiery zeal directed to a right end. POLYCARP, the disciple of John, told contemporaries of IRENÆUS, who narrates the story on their authority, that on one occasion when John was about to bathe, and heard that Cerinthus, the heretic, was within, he retired with abhorrence, exclaiming, Surely the house will fall in ruins since the enemy of the truth is there.

For he that biddeth him God speed - That gives him any encouragement, is accessory to his evil deeds.