INTRODUCTION TO THE THIRD LETTER OF JOHN
The things said about the Second Letter of John apply here also. Traditional history makes Gaius the one who wrote down The Gospel of John, and identifies him as the Gaius of Corinth (Romans 16:23; 1 Corinthians 1:14). He was probably an evangelist (see note on Ephesians 4:11), and probably a church elder as well (tradition places him in the church at Pergamum).
There was trouble in the congregation of which he was part. Diotrephes, who may have been a church elder also, refused to welcome some evangelists sent by John. This seems to imply that he rejected the authority of John, and this causes some to think Diotrephes was a "Paulite" (see 1 Corinthians 1:12 and note). John writes this Letter to praise the action of Gaius (2 John 1:5-8), and to show his intention to come personally to deal with the false teachers. If Pergamum is the church where Gaius receives this letter then Diotrephes is probably a Nicolaitan teacher (see Revelation 2:14-15 and notes).
Both Paul and John operated "Schools of Preaching," in the sense that they took promising young men and trained them to do the work of an evangelist (compare 2 Timothy 4:5 and note). It is probable that all the apostles trained large numbers of such preachers and teachers to fill the needs of the Christian ministry.
John probably wrote from Ephesus to churches in the area, and the time is probably the last decade of the first century.