3 John 1:3

For I rejoiced greatly when the brethren came - Who these were is not certainly known. They may have been members of the same church with Gaius, who, for some reason, had visited the writer of this Epistle; or they may have been the “brethren” who had gone from him with a letter of commendation to the church, 3 John 1:9, and had been rejected by the church through the influence of Diotrephes, and who, after having been hospitably entertained by Gaius, had again returned to the writer of this Epistle. In that case, they would of course bear honorable testimony to the kindness which they had received from Gaius, and to his Christian character.

And testified of the truth that is in thee - That you adhere steadfastly to the truth, notwithstanding the fact that errors abound, and that there are many false teachers in the world.

Even as thou walkest in the truth - Livest in accordance with the truth. The writer had made the same remark of the children of Cyria, to whom the second Epistle was directed. See the notes at 2 John 1:4.