1 John 3:19Meaning & Commentary from the Church Fathers

And by this we know that we are of the truth: by loving the brother not in word, but in deed and truth. How do we know? In this way: one who says one thing and does another, not making deed agree with word, is a liar and is not truthful. "And shall assure our hearts before Him." This means that through truthfulness, for truth will be in us when our deeds correspond to our words, we shall calm our conscience. By "heart" he means conscience. How shall we calm it? By placing ourselves in such a position that we speak our words before God as witness. This is what "before Him" means. If, he says, we do not do so, and our conscience or heart condemns us, then it is evident that we sin. Therefore we know that we are of the truth, that is, of God.

The more a man remembers this rule, and the more he strives to make his words agree with his feelings and deeds, the more right he has to be called a true Christian. He may say of himself with David, "I have set the Lord always before me, for He is at my right hand" (Ps 14:8). But if a man's state is such that his own conscience cries out against him, accusing his words and deeds, then he is pitiable. For he is far from the path of salvation. Already condemned by his own conscience, he will be condemned sevenfold by Him before whom all things are naked and laid bare (Heb 4:13).

“By this we know that we are of the truth.” True love in us serves as a sign of our high inward dignity. It enables us to be assured that we are of the truth, that is, of God. Jesus Christ tells Pilate that He came into the world to bear witness to the truth. He also says that only those who are of the truth hear Him (Jn 18:37). “And before Him we humble,” in Russian, “we reassure,” “our hearts.” The reassurance of the heart is the fruit of our love for neighbors.

"By this we know that we are of the truth": if we love not in word and tongue, but in deed and truth, there is in this an indisputable testimony for us ourselves that we are of the truth. By this very thing we ourselves know, that is, we are assured, not conjecturally, but certainly and truly, by the inward witness of spirit and conscience. We know that we are of the truth, not hypocrites, liars, or deceivers, but true Christians who rightly believe and confess Christ's truth. We know that we have known the truth, that is, God the Father and the Lord Christ (Jn 17:3). We know that we have been born of God and have become sons of God (1 Jn 3:9), and have passed from death into life (v. 14).

The consequences of our sonship before God. The first consequence is peace of conscience (1 Jn 3:19-22). If we love not in word or tongue, but in deed and truth, as befits the children of God, not merely in name and by Christian title alone, but in very truth, or as the Apostle says, if "we are of the truth," then "we shall assure our hearts before Him," before God (1 Jn 3:19). By the word "hearts" the Apostle means conscience (Theophylact). To explain the greatness of this great inward good of the children of God, the Apostle, according to his custom, uses a comparative contrast. He compares the judgment of our conscience with the judgment of God. If the first judgment is heavy, the second is of course incomparably heavier.

After indicating the general character of Christian love, the Apostle John shows certain kinds and manifestations of love, namely mercy toward the poor, from whom the rich often turn away both heart and eyes. Then the Apostle teaches everyone in general not to stop at love only in the heart, still less at words, but necessarily to pass on to the manifestation of love in actual deed. Only one who lives by active love, embracing his whole being, lives the true life and can stand before God's judgment with a peaceful conscience. "Where there is love," says Saint John Chrysostom, "there is neither envy nor slander.