Author:John the Apostle is traditionally identified as the author of 3 John (see the introduction to the book of 1 John, p. 241).
Audience:This Epistle was written to Gaius, a faithful member of the Church. It was the custom of early Church members to take Christian missionaries into their homes and provide for their needs. John praised Gaius for his unselfish devotion to the cause of Christ in providing accommodations for God’s traveling servants.
Historical Background:In addition to the problem of false teachers traveling around and deceiving the Saints (see the introduction to the book of 2 John, p. 243), some Church leaders served for personal ambition rather than for the love of Christ or His Saints. Diotrephes was one such erring leader. He was guilty of trying to assert his authority over that of an Apostle.
Theme:John wrote to compliment Gaius for his faithfulness and encourage him. John also wanted to indirectly warn Diotrephes.