The elder unto the wellbeloved Gaius, whom I love in the truth.
Caius was probably that Caius of Corinth whom St. Paul mentions, Romans 16:23. If so, either he was removed from Achaia into Asia, or St. John sent this letter to Corinth.
 For I rejoiced greatly, when the brethren came and testified of the truth that is in thee, even as thou walkest in the truth.
For — I know thou usest all thy talents to his glory.
The truth that is in thee — The true faith and love.
 I have no greater joy than to hear that my children walk in truth.
I have no greater joy than this — Such is the spirit of every true Christian pastor.
To hear that my children walk in the truth — Caius probably was converted by St. Paul. Therefore when St. John speaks of him. with other believers, as his children, it may be considered as the tender style of paternal love, whoever were the instruments of their conversion. And his using this appellation, when writing under the character of the elder, has its peculiar beauty.
 Beloved, thou doest faithfully whatsoever thou doest to the brethren, and to strangers;
Faithfully — Uprightly and sincerely.
 Which have borne witness of thy charity before the church: whom if thou bring forward on their journey after a godly sort, thou shalt do well:
Who have testified of thy love before the church — The congregation with whom I now reside.
Whom if thou send forward on their journey — Supplied with what is needful.
Thou shalt do well — How tenderly does the apostle enjoin this!
 Because that for his name's sake they went forth, taking nothing of the Gentiles.
They went forth — To preach the gospel.
 We therefore ought to receive such, that we might be fellowhelpers to the truth.
To receive — With all kindness.
The truth — Which they preach.
 I wrote unto the church: but Diotrephes, who loveth to have the preeminence among them, receiveth us not.
I wrote to the church — Probably that to which they came.
But Diotrephes — Perhaps the pastor of it.
Who loveth to have the preeminence among them — To govern all things according to his own will.
Receiveth us not — Neither them nor me. So did the mystery of iniquity already work!
 Wherefore, if I come, I will remember his deeds which he doeth, prating against us with malicious words: and not content therewith, neither doth he himself receive the brethren, and forbiddeth them that would, and casteth them out of the church.
He prateth against us — Both them and me, thereby endeavouring to excuse himself.
 Beloved, follow not that which is evil, but that which is good. He that doeth good is of God: but he that doeth evil hath not seen God.
Follow not that which is evil — In Diotrephes.
But that which is good — In Demetrius.
He hath not seen God — Is a stranger to him.
 Demetrius hath good report of all men, and of the truth itself: yea, and we also bear record; and ye know that our record is true.
And from the truth itself — That is, what they testify is the very truth.
Yea, we also bear testimony — I and they that are with me.
 But I trust I shall shortly see thee, and we shall speak face to face. Peace be to thee. Our friends salute thee. Greet the friends by name.
Salute the friends by name — That is, in the same manner as if I had named them one by one. The word friend does not often occur in the New Testament, being swallowed up in the more endearing one of brother.