It was a scholar named Martin Hengel who suggested that John’s letters made more sense to read in reverse order than to read them in the order we find them. The letters we call 1, 2, and 3 John—like other letters in the New Testament—are in their current order because of their length, not because of their chronological order. We cannot prove it, but it is a reasonable suggestion.
For example, 3 John involves tensions, but it does not indicate that any split has yet taken place, such as we see in 1 John 2:19. Unfortunately, we cannot know if 3 John is written to the same community or if Diotrephes is part of the group that will eventually split off from John’s group. What we can say is that it is a letter of recommendation from "the elder" to someone named "Gaius" in a certain church.
We are going with the suggestion that "the elder" here is someone we know as John the elder, an early follower of Jesus from Judea who was not one of the twelve original disciples. John the elder encourages Gaius, who is a leader in the church to which John is writing, to receive a traveling teacher coming his way. The name of this traveling teacher is Demetrius.
An elder, as we mentioned in the chapter on 1 Peter, was one of several older individuals who led an ancient congregation. Most congregations in the early church were probably run by a group of elders, also called overseers.  It is at least possible that both Gaius and Diotrephes were both elders in the church to which John wrote, although it is possible they are in nearby congregations.
We might pause for a moment and point out that the first century churches were structured to fit a first century context. The "descriptions" of the early church are not "prescriptions." For example, it is hard to know how often these local gatherings, usually house churches, had a primary leader like what we call a pastor, a senior pastor, or a lead pastor. But we don't have to spend a lot of time trying to nail down the answer to this question.
The way you best structure leadership has everything to do with the context and function of an organization. It would be foolish to think that there is just one church organization for all time, and that we have to figure out exactly what it was in the New Testament church so we can mimic it. What if we were to find that there was more than one way of structuring a church even in the New Testament? What if we were to find that early church organization itself was simply mimicking the organization of synagogues and voluntary associations around it? We might find that rather than imitating some timeless divine organizational chart, we were simply imitating Jews and Romans who lived two thousand years ago.
Indeed, is it possible that some of the problems in the church 3 John addresses came from the fact that there was no focal leader? John is fighting for the soul of the church by sending them a temporary teacher. We are reminded of how the old Methodists had circuit riders who went from congregation to congregation preaching on a "circuit." The revivalist movement also had traveling evangelists who could come to a town and preach for a week or two before moving on.
So the early church had "itinerant teachers" like Demetrius, whom John was sending. Demetrius would be something like a Methodist preacher sent to a congregation for a year or at least several months. In that sense, John is functioning something like a bishop in the Methodist church today. The difference is that there is no broader church structure at this time to give John official authority. He has to rely on his "charismatic" authority and personal relationship with Gaius to get Demetrius into the church. 
John is sending Demetrius because he wants the good of the church, but there is no question that he is creating conflict. He is going behind the back of one leader in the church by making a connection with another leader in the church. Normally, this would be a deeply divisive and probably inappropriate thing to do. What is different in this case is John's status is perhaps that of an apostle. 
We also learn in 3 John that a group is just leaving Gaius' community (3). It is not entirely clear whether they were "ministers." John calls them "strangers," perhaps suggesting that they were just passing through, perhaps on their way from teaching somewhere else. But it seems clear that Diotrephes did not welcome them. Diotrephes will not welcome anyone associated with John (9). He is spreading "malicious nonsense" about John.
The question of how to deal with stubborn leaders in local churches is as fresh as last Sunday. In a world without apostles, one advantage of having a focal leader in a local church and leaders beyond the local church is that there are lines of authority that can address trouble makers like Diotrephes. There are also, of course, disadvantages to having regional or local leaders that are too powerful.
The problem is fallen human nature. Many of us enjoy power a little too much and, as the saying goes, "Power corrupts, and absolute power corrupts absolutely." This is why I personally think the "presbyterian" structure of church governance works the best, especially in a democratic culture like America. In this system, local churches elect a focal leader, and their representatives elect regional leaders. These leaders then have power but not unlimited power. There are checks and balances that counteract the deficiencies of structures where either there is almost only local power (the congregational system) or is heavy regional power (the episcopal system). 
So John is using his connection with Gaius to try to get a good teacher into his community, a man named Demetrius. John describes Demetrius someone "well-spoken of" (12) and, because his message is true, the truth speaks well of him. Further, John's "testimony is true," and he speaks well of him. It is quite possible that Demetrius himself delivered this letter to Gaius.
At the time of 3 John, the conflict with Diotrephes had not reached a head. He remained in the church causing problems and slandering John's authority. John was in the process of trying to win over the congregation and correct false ideas. He had sent teachers there and was soon going to come himself. But the worst was still yet to come.
As a final note on 3 John, wouldn’t it be great if it could be said of all church ministers that the truth spoke well of them? What if the words of those who preached the word today had the ring and air of truth to them? Let us pray for the Lord to give us ministers such as these!
 The Johannine Question.
 The word overseer in Greek is episkopos and very quickly came to be associated with an individual leader over several congregations in a city, then later in a region. However, in the New Testament, there seems to be little difference between an elder (presbyteros) and an overseer. See Titus 1:6-7 where the words are used interchangeably.
"Charismatic" authority, in this context, is authority based on the charisma of an individual. This is an authority that does not come from having an official position or title but from being recognized as having informal authority by a group of people. Someone may have a position but no one listen to him or her, yet someone else may have no position at all and yet everyone follow their lead. Prophetic authority in the early church was a kind of charismatic authority.
 We don't actually know if John saw the risen Jesus, which would make him an apostle. He is never called that, however.
 In the congregational system (such as Baptists), local churches are more or less completely self-controlled. The local church decides what it will believe and who its pastor is. The local church even ordains ministers. In an episcopal system (such as Catholics or Anglicans), bishops are appointed for life and have the authority to ordain, to appoint ministers to churches, and so forth.