Towards the end of the first century, the churches in and around Ephesus suffered much tension and conflict because of false teaching (e.g. Rev 2:2-6; cf. Acts 20:17,29-30). Early records indicate that the apostle John lived in Ephesus at this time, and that he wrote his Gospel and three letters partly to counter some of the false views.
Background and contents of 3 John
In spite of his warnings about travelling preachers who had wrong teaching (2 John 10-11), John knew that many other travelling preachers were genuine Christians whose teaching was true and wholesome. But there was a problem in one church because a dictatorial person named Diotrephes refused to accept the travelling preachers into the church. He considered them representatives of John, whom he opposed. John therefore wrote a letter (3 John) to one of the better leaders in the church, a friend named Gaius, to encourage and help him. In the letter John encouraged Gaius to keep helping the true preachers of the gospel (v. 1-8). He assured Gaius that if Diotrephes persisted in his present attitudes, then he himself would deal with him when he visited the church in the near future (v. 9-15).