1 John 3:3

And every man that hath this hope in him
Or on him, Jesus Christ; for a true hope of that eternal happiness, which lies in likeness to Christ, and in the vision of him, is only founded on his person, blood, righteousness, and sacrifice: and this hope every man has not, only he who is born again; for this grace is implanted in regeneration, when men are of abundant mercy begotten unto it, and have it bestowed upon them as a free grace gift; and which is of great service to them both in life and in death; and among the rest it has this influence and effect upon them, that every such person that has it,

purifieth himself even as he is pure;
not that any man can purify or cleanse himself from sin, this is only owing to the grace of God and blood of Christ; nor that any man can be so pure and holy as Christ is, who is free from all sin, both original and actual; but this must be understood either of a man that has faith and hope in Christ, dealing by these with the blood of Christ for purity and cleansing, with whom and which these graces are conversant for such purposes; or of such a person's imitating of Christ in the holiness of his life and conversation, making him his pattern and example, studying to walk as he walked; to which he is the more excited and stimulated by the hope he has of being a Son of God, a dear child of his, and therefore ought to be a follower of him, and walk as Christ walked, in humility; love, patience, and in other acts of holiness; and by the hope he has of being like unto him, and with him in the other world to all eternity: but then this "as" is only expressive of some degree of likeness and similitude, and not perfect equality, which is not to be expected in this, or in the world to come; believers indeed, who have faith and hope in the justifying righteousness of Christ, may, and should consider themselves pure and righteous, and free from sin, as Christ is; being clothed upon with his robe of righteousness, in which they stand without fault before the throne, without spot or wrinkle, or any such thing; but this does not seem to be the sense of the place here, the argument being to engage the saints to purity and holiness of life and conversation, from the consideration of the great love of God bestowed upon them in their adoption, and from their hope of eternal happiness, as the context shows; see ( 2 Corinthians 7:1 ) ; other arguments follow.