Verse 19. - In this; or, hereby ἐν τούτῳ, here clearly refers to what precedes; and the thought is similar to that in verse 14. By sincere and active love we shall come to know γνωσόμεθα that we are children of the truth. "The truth" here is almost equivalent to "God;" and we seem to have here an echo of Christ's words to Pilate, "Everyone that is of the truth heareth my voice" (comp. 1 John 2:21; John 3:31; John 8:23, 47, etc.). The construction in what follows contains several doubtful points:

(1) whether πείσομεν is coordinate with γνωσόμεθα or ἐσμέν;

(2) if the former, whether ἐν τούτῳ goes on to πείσομεν, or is confined to γνωσόμεθα;

(3) whether we should read ὅ τι ἐάν or ὅτι ἐὰν.

In all three cases the first alternative is perhaps preferable: And hereby we shall persuade our heart before him (that we are of the truth, and therefore have nothing to fear), whereinsoever our heart condemn us. But on the third point see Dr. Field's note in 'Otium Norvicense,' pars 3. Before him is very emphatic; it is in God's sight that the children of the truth are able to quiet their hearts, not merely in their own eyes. (For πείθω used absolutely, comp. Matthew 28:14; Acts 12:20; 2 Corinthians 5:11.)

3:16-21 Here is the condescension, the miracle, the mystery of Divine love, that God would redeem the church with his own blood. Surely we should love those whom God has loved, and so loved. The Holy Spirit, grieved at selfishness, will leave the selfish heart without comfort, and full of darkness and terror. By what can it be known that a man has a true sense of the love of Christ for perishing sinners, or that the love of God has been planted in his heart by the Holy Spirit, if the love of the world and its good overcomes the feelings of compassion to a perishing brother? Every instance of this selfishness must weaken the evidences of a man's conversion; when habitual and allowed, it must decide against him. If conscience condemn us in known sin, or the neglect of known duty, God does so too. Let conscience therefore be well-informed, be heard, and diligently attended to.And hereby we know that we are of the truth,.... By the saints loving one another in deed and in truth, they know, as the cause is known by the effect, that they are of God, who is the true God, the God of truth, and cannot lie, and is truth itself; that they are the children of God, and are born of him, since they love those that are, and every like loves its like; and that they are of Jesus Christ, who is the way, the truth, and the life; that they belong to him, are his, since they have his Spirit, as appears by his fruits in them, and this, among the rest, love to the brethren; and that they are his disciples, which others, even all men know, as well as themselves, by their mutual brotherly love; and that they are of the Gospel, which is truth, and the word of truth; that they are begotten, and born again, according to the will and grace of God by it, and are on the side of it, and can do nothing against, but all for it; and that they are true, sincere, and upright persons, true believers in Christ, whose faith works by love, and are real lovers of him, and his, since they love not in word only, but in deed and in truth.

And shall assure our hearts before him; or "persuade our hearts": arrive to a full assurance of faith, hope, and understanding, that we are of the truth, do belong to God, are loved by him with an everlasting love, are chosen by him unto salvation, and are his adopted and regenerated ones, having passed from death to life, of which brotherly love is a sure evidence, 1 John 3:14. Some render the words "shall pacify", or "make our hearts tranquil": or "quiet"; this only the blood of Christ can do, and does, being sprinkled on the conscience: he only has a quiet mind, or true peace of conscience, that looks to the righteousness of Christ for justification, and deals with his blood for the full and free remission of his sins: it is true indeed, that one that loves his brother heartily and sincerely, has peace of mind in it, though not for it; when, on the other hand, there is no peace to the wicked man, that hates his brother; for where there is envying, malice, hatred, and strife, there is no true peace, pleasure, and comfort, but confusion, uneasiness, distraction, and every evil work. Or this passage may refer to that holy confidence before God, which true believers in Christ, and cordial lovers of the brethren, have; both now at the throne of grace, where they can come with boldness, intrepidity, and freedom, to ask for what they want, and confidently believe they shall receive what is proper and needful for them; and also hereafter, at the throne of judgment, and in the day of judgment, when they shall have boldness, and not be ashamed before the Judge at his coming; who will particularly take notice of their love in feeding, clothing, and visiting the least of his brethren, which he takes as done to himself.