Nothing is known of the Gaius to whom 3 John is written save what the letter itself tells us. But this is no great loss, for all we need to know is apparent from the text. The New Testament knows of a number of other men named Gaius. There is a Gaius of Macedonia, who together with Aristarchus was seized by the rioting mob at Ephesus (Acts 19:29). There was a Gaius who accompanied Paul on his last trip to Jerusalem and who formed part of the group of delegates which presented the offering from the Gentile churches to the church in Judea (Acts 20:4). This Gaius was from Derbe and presumably represented that church and possibly the other churches of Galatia. Finally, there was the Gaius of Corinth in whose house Paul lived while dictating the letter to the Romans (Rom. 16:23). But Gaius was a common name, and there is no reason to identify any of these persons with the Gaius of 3 John. According to 3 John this Gaius was simply a faithful and spiritual Christian leader in a local church over which the apostle John had oversight.
But troubles had come into this church and, in spite of a letter sent by John to the chief offender, the problems had apparently grown worse. To begin with, a man named Diotrephes had assumed an unwarranted and pernicious authority in the church, so much so that by the time of the writing of this letter John’s own authority had been challenged and those who had been sympathetic to John had been excommunicated from the local assembly.
Moreover, due to this struggle, traveling missionaries had been rudely treated, including quite probably an official delegation from John. Gaius had received such persons and is here commended for it. Diotrephes had not and is rebuked. Diotrephes is also promised further chastisement when the apostle comes to him, which he hopes to do shortly. Toward the end of the letter a third personality is mentioned, Demetrius, whom the apostle holds up as an example of one who does good and is therefore clearly of God.
The messages to or about these three personalities give a straightforward outline to the book. There is: 1) the message of Gaius, who is termed a fellow worker; 2) the message about Diotrephes, who is causing the problem; and 3) the message about Demetrius, who is designated as an example to all.
Two characteristics of Gaius stand out, his truth and his love, and John deals with each in turn. Gaius had obviously heard the truth of the Gospel and had received it wholeheartedly with the result that the truth was now in him and was causing him to pursue vigorously that way of life which the truth indicated. Moreover, this was not some hidden or secret thing. For, on the contrary, Gaius lived the truth in such an open way that he was observed by others who in turn reported the uprightness of his conduct and character to John. He was “a light” in this world, as Jesus had instructed his disciples to be. He had fulfilled the Lord’s injunction, “Let your light so shine before men, that they may see your good works, and glorify your Father, who is in heaven” (Matt. 5:16).