Commentary on the Epistle of St. John the Theologian:
1:4. And these things write we unto you, that your joy may be full.
Through life in the Holy Trinity, through communion with the Father, the Son, and the Holy Spirit, man’s being is filled with true joy, which is nothing other than divine blessedness. Without this, man’s being is filled with grief, sorrow, and woe. If not with that, then what can death- and even before death, sin- fill the human being? A current of bitterness, or sinful pleasures that gradually change into bitterness, pours forth into the soul through every sort of sin. In every case, through each sin committed, at least a drop of bitterness falls on the soul and imperceptibly spreads throughout the soul. When the time comes, it grows into an enormous sorrow, and man, very often, does not even know where this grief in his soul and heart comes from. Through communion with Christ and His holy virtues, man’s being is filled with unceasing joy. Through living the love of Christ, man’s being is filled with inexpressible joy, as well as from living the righteousness of Christ, the goodness of Christ, the humility and meekness of Christ. And when man looks into himself- behold, he is completely filled with divine joy, and there is not a trace of grief or fear of death in him. Therefore, the holy Theologian proclaims: And these things write we unto you, that your joy may be full (πεπληρωμένη).
Taken from the book:
Archimandrite Justin Popovich, Commentary on the Epistles of St. John the Theologian.