The apostle himself, a little earlier in this same epistle (1 Jn 1:8-10; 1 Jn 2:1-2; 1 Jn 3:3), teaches that a believing man sins and cannot but sin.
He must confess his sins to the Lord, and can receive forgiveness for them. Therefore the present passage is not speaking about the sinlessness of the believer who abides in Christ.
Throughout this section the apostle speaks of sin in an intensified sense. He speaks in the sense in which he later speaks of sin unto death (1 Jn 5:16-17).
Every sin is lawlessness, but not every sin threatens deprivation of salvation. There are sins of weakness, unavoidable for man while he is in this body, which exist in him despite his whole desire not to sin.
It is not of these that the apostle said, “he does not sin.” Rather, he speaks of prevailing sin, or of enslaving sinfulness. Of the man who sins in this way he says that he has not seen Christ and has not known Him.
The one who abides in Christ does not sin in the sense that he does not give himself into slavery to sin. With all his strength he strives to withdraw from sin, struggles against it, and overcomes it.
Though he falls, he hastens to confess his sin (1 Jn 1:10), and does not serve it as an idol. Everyone who abides in Christ does not sin, yet “he who says he has no sin deceives himself” (1 Jn 1:8).
A Christian, a child of God, bears a contradiction within himself in his life on earth. On the one hand, he is a sinner and sins continually and irresistibly (Rom 7:15-24).
On the other hand, he is truly free from sin (Rom 6:18), free to such a degree that he cannot even sin; verse 9, see note.
In reality he has finished with sin; sin has become wholly alien to him. Yet in manifestation it still lives in him and will live until his temporal death; see Romans chapter 7.
Whoever is born of God in Christ is a new creation. In him the old has passed away and all has become new (2 Cor 5:17). Yet sin lives in him (Rom 7:17), though the one born of God cannot sin (Rom 7:9).
Therefore, the one who abides in Christ does not sin. But everyone who sins has neither seen Him nor known Him. He has not seen Him with the eyes of faith and spirit.
He has not known Him with the eyes of an enlightened mind. Darkened by sin, he does not see Him, for only the pure see Him. He has not known Him, and there is no light of reason in his knowledge.
“Sin,” says the apostle, “has no place in you. For Christ appeared to destroy sin, and as He Himself had no share in sin, so also for you, who have been united with Him and established by faith in Him, there remains no place for sinning.
This is what the words mean: everyone who abides in Him does not sin. Then, having said that the Son of God appeared, and that He appeared so that, not having committed any sin of His own, He might take away, that is, destroy, our sin, he adds: everyone who sins has not seen Him.
If, he says, when He appeared, you saw Him and, as a result of seeing Him, received strength not to yield to sin, as those perfectly established in Him, then it is evident that those who sin have not seen Him and therefore have not known Him.
By seeing Him, he does not mean seeing by a simple contact of the eye, nor a slight reproduction in one’s imagination of something known. He means the unwillingness to consider the matter at all, to learn it, and to be joined to Him” (Theophylact).
THEOSIS