Having exposed Diotrephes to apostolic censure, and warned against his uncharitable dealings, John admonishes Gaius to take a different course.  Diotrephes pursued that which was evil, hating his brethren and rejecting apostolic authority.  Gaius, on the other hand, should refuse that which was evil, but follow after the truth and good principles.  To show Christian charity in spite of the opposition of Diotrephes seems to be the direction in which John is urging him.  And in order to buttress the exhortation, John issues a sober reminder of the eternal importance of these vital matters.  The person who does good is of God.  A clean heart has been created in him by the power of the Holy Ghost, and he strives to follow after that which is good.  This was undoubtedly the character of Gaius, but John thought it not worthless to urge him on in his pursuit of holiness.

The opposite side of the coin is where one would find Diotrephes and all his ilk.  The man who does evil has not seen God.  God has never been revealed to his heart in a saving fashion.  He may have much religious knowledge, and even be able to claim marvelous experiences, but by his fruits he is known.  Christ Himself warned that many prophets and miracle workers will be cast away from His presence at the last, because they were workers of iniquity.  No person whose life is void of the pursuit of holiness, but persists in following his own evil inclinations, has seen God, nor will he ever view God’s face with joy.