That day of Christ’s return will see the perfection of God’s eternal purpose concerning His chosen ones. Here F. F. Bruce writes brilliantly:
These first two verses of 1 John 3 celebrate the accomplishments of God’s eternal purpose concerning man. This purpose finds expression in Genesis 1:26, where God, about to bring into being the crown of creation, says, “Let us make man in our image, after our likeness.” In other words, he declares his intention of bringing into existence beings like himself, as like himself as it is possible for creatures to be like their Creator… But Genesis 3 tells how man, not content with the true likeness to God which was his by creation, grasped at the counterfeit likeness held out as the tempter’s bait: “you will be like God, knowing good and evil.” In consequence, things most unlike God manifested themselves in human life: hatred, darkness and death in place of love, light and life. The image of God in man was sadly defaced. Yet God’s purpose was not frustrated; instead, the fall itself, with its entail of sin and death, was overruled by God and compelled to become an instrument in the furtherance of his purpose.
In the fulness of time the image of God, undefaced by disobedience to his will, reappeared on earth in the person of his Son. In Jesus the love, light and life of God were manifested in opposition to hatred, darkness and death. With his crucifixion it seemed that hatred, darkness and death had won the day, and that God’s purpose which had survived the fall, was not effectively thwarted. But instead, the cross of Jesus proved to be God’s chosen instrument for the fulfillment of his purpose…. This purpose is stated by Paul in terms which go back far beyond the act of creation in Genesis 1: “those whom he foreknew he also predestined to be conformed to the image of his Son, in order that he might be the first-born among many brethren” (Rom. 8:29). The children of God, who enter his family through faith in his Son, display their Father’s likeness, because of their conformity to him who is the perfect image of the invisible God.1
Now, as God’s children, we are made like Christ progressively as we behold him, as it were “in a mirror, darkly” (1 Corinthians 13:12). In that day we shall be fully like him, for we shall see him “face to face.”
After such rapturous thoughts the Christian is in danger of floating away on a cloud of mysticism, but John does not allow this. Nor does Scripture allow it anywhere. “Is this your hope?” John seems to ask. “Then show it,” he concludes. For everyone who thus hopes in Him “purifieth himself even as he is pure” (v. 3).
This is what one writer calls the “all-important corollary of the Christian hope.”2 It is simply that if we are to be like Christ hereafter, then we must act like Christ now, imitating Him now, particularly in the area of our personal morality. Moreover, it is not even a mystical and somehow glorified Christ that we are to imitate; for John admits that he does not yet know what we shall be, having not yet seen Christ face to face in His glory. The Christ we are to imitate is the Christ of history. It is the Christ of the opening pages of the epistle, the Christ who was seen and heard and touched and indeed proclaimed from the beginning as the heart of the apostolic Gospel. That is the Christ who is coming back and to whom we must answer for how we have lived. He who truly hopes in Him will live for Him. He who has truly known Him will seek to be like Him.
1F. F. Bruce, The Epistles of John (Old Tappan, NJ: Revell, 1970), 85-86.
2C. H. Dodd, The Johannine Epistles (London: Hodder and Stoughton, 1946), 71.