3 John 1:8

We, therefore, ought to receive such, that we might be fellow-helpers to the truth.

The apostle here specifies the virtue in which Gaius excelled: Beloved, thou art acting as a faithful brother in rendering service to the brethren, strangers at that. It was an act of faithfulness agreeing well with the faith Gaius was professing which he performed when he rendered such signal service to the brethren, who were total strangers to him, at that. He had not known them before, he was bound to them by no external ties, but the fact that they were believers with him, as the letters of John showed, was a sufficient incentive to him to receive them with open arms and to do all in his power to make their journey and their stay a pleasant one.

It was from some of these brethren that St. John had received the report which occasioned this letter: Who testified to the love before the congregation; and thou wilt do well in speeding them on their journey in a manner worthy of God. So great was the impression which the cordial hospitality of Gaius made upon the missionaries that they reported it at once upon their return.; they were effusive in their commendation of their host, of the love which he had shown them. In acknowledging this, the apostle incidentally provides for a future continuance of this charitable endeavor: If Gaius continues this policy of assisting the missionaries by speeding them on their way, and in a manner worthy of their calling of ministers of God, then he will do well. See Acts 15:26. For, as John says, it was for the sake of His name that they went out and did not accept anything from the heathen. These missionaries, like all men worthy of the name, did not go out to seek their own glory and advancement. They were concerned only about the Word of the Gospel, about extolling the name of Jesus Christ as the Savior of the world. They were preaching without receiving any compensation from the heathen, probably in order not to bring suspicion upon their office as though they were merely in the business of preaching for the sake of the money they might make that way. This being the case: We, therefore, are under obligation to support such men, that we may prove fellow-workers with the truth. That is the duty of the Christians at all times and in all places, to provide for the bodily necessities of men that are going forth to preach the Gospel. In this way the Christians perform their share with the truth and for the truth of the Gospel, they assist in spreading the glorious news of salvation through the redemption of Jesus Christ.