3 John was written shortly after 1 and 2 John toward the end of the first century A.D. It may be that 3 John was written after the book of Revelation. If that is the case, then 3 John is the last of John’s inspired writings.
John addresses this third epistle to Gaius. While there are other people mentioned by this name in the New Testament it is likely that this Gaius is distinct from those previously mentioned. The third epistle of John gives us all we know about this Gaius. He seems to have been a pastor.
John writes to commend Gaius and another individual named Demetrius. But the primary purpose of this letter seems to be John’s warning about a person named Diotrephes. While Gaius is a picture of generosity, Diotrephes is a picture of pride. The problem with Diotrephes is not doctrinal. The problem with Diotrephes is practical.
Truth, to be worth something, must be put into practice. Faith without works is dead (James 2). God has prepared good works for us to do (Ephesians 2:10). And so in 3 John we look at the practice of truth or true practice.