Third John is a letter thanking Gaius for his hospitality in accepting several traveling teachers sent by John to Gaius’ church. 3 John calls these itinerant teachers “strangers” who ought to be given hospitality in “a manner worthy of God.” Like 2 John, this is more of a “note” than a letter, likely filling a single small sheet of papyri (v. 13). It is possible that this letter was delivered by Demetrius as a kind of “letter of introduction” indicating that he in fact has the blessing of John the Elder.
Didache 12 gives instructions on how a church ought to handle a traveling teacher. If a person visits the church and “comes in the name of the Lord,” he is to be welcomes. But, the writer warns, he ought to be examined to find out if he has true insight. If he “merely passing through,” the church ought to assist the teacher, but only if he stays no more than a day or two. If he is a genuine prophet, he is “worthy of his food,” the church ought to share with him and help him with his ministry (13:1-3)
One of these teachers was apparently refused by Diotrephes, another believer in the church. Diotrephes’ behavior is condemned by John as being “un-brotherly.” Gaius is praised for his kind treatment of another teacher, Demetrius, who probably was the deliverer of this letter. We have no idea why Diotrephes refused a teacher. Perhaps he examined him and judged him unworthy to teach. It is also possible that shabby treatment of Demetrius is a reflection on John’s authority – Diotrephes disrespects John as the elder / bishop and therefore refused to give hospitality to his representative. Jobes suggests that Diotrephes is “on the side of the antichrists,” although this cannot be proven conclusively (Letters to the Church, 445).
This letter gives us an insight into how the small house churches of the first century functioned, and to some extent the problems with a house church. An individual could see the church as very much their own and “run things” far too autocratically. Diotrephes is free to make decisions about who may speak to his congregation, trumping John’s authority in this case. There is no “committee of elders” in the church to discuss and decide the matter. The idea of a “church board” is very much a modern congregational church invention.
John the Elder clearly believes has authority over this church and authorized teachers to visit the churches from time to time. He expects his elders to accept the teachers and give them proper hospitality when they visit. Perhaps we can describe him as a “bishop,” but if the tradition of equating John the Disciple / Apostle with John the Elder is correct, this might be an example of apostolic authority.
This teaching on hospitality in Third John also is difficult to apply in a modern context. I suppose it might be “applied” by being kind to traveling missionaries when they visit your church, but I think that is a rather limited application. There is a rigorous “testing” of the visiting teacher implied by this letter – how does that work in a modern context?