Adam Clarke's Commentary on the Bible

Verse 10 (2 John 1:10)

If there come any unto you - Under the character of an apostle or evangelist, to preach in your house; and bring not this doctrine, that Jesus is come in the flesh, and has died for the redemption of the world.

Receive him not unto your house - Give him no entertainment as an evangelical teacher. Let him not preach under your roof.

Neither bid him God speed - Και χαιρειν αυτῳ μη λεγερε· And do not say, Health to him - do not salute him with Peace be to thee! The usual salutation among friends and those of the same religion in the east is, Salam aleekum , "Peace be to you;" which those of the same religion will use among themselves, but never to strangers, except in very rare cases. This is the case to the present day; and, from what John says here, it was a very ancient custom. We have often seen that peace among the Hebrews comprehended every spiritual and temporal blessing. The words mean, according to the eastern use of them, "Have no religious connection with him, nor act towards him so as to induce others to believe you acknowledge him as a brother."

- Adam Clarke's Commentary on the Bible