Commentary by St. Justin (Popovich) on the First Epistle of St. John the Theologian:
3:3. And every man that hath this hope in Him purifieth himself, even as He is pure.
Whoever has as his goal and purpose to be an image of Christ and to be Christ-like purifieth himself through the help of the divine powers of the Holy Mysteries and the holy virtues. His unchanging ideal is to become even as He is. To realize this, he places all his hope in Him, Who is infinitely loving and gives purpose to everything. Purify yourself, even as He is pure; make yourself holy even as He is holy (cf. I Pet. 1:15-16); make yourself love as He is Love; make yourself merciful as He is merciful. For He became as we are, so that we would become as He is. He is the fullness of the Godhead bodily (Cor. 2:9), so that we may become the fullness of the Godhead spiritually, in a grace-filled manner. He became man, so that we would be gods. He cleanseth us from all sin (I John 1:7), so that we would become pure even as He is pure. This is the purity He gives and expects from us. A human being is not meant for sin and its impurity, but for God and His purity.
Excerpt taken from the book:
Commentary on the Epistles of St. John the Theologian, By: St. Justin Popovich