And hereby we know, or, by this we know. The word truth, he takes now in a different sense; but there is a striking similarity in the words, -- If we, in truth, love our neighbors, we have an evidence that we are born of God, who is truth, or that the truth of God dwells in us. But we must ever remember, that we have not from love the knowledge which the Apostle mentions, as though we were to seek from it the certainty of salvation. And doubtless we know not otherwise that we are the children of God, than as he seals his free adoption on our hearts by his own Spirit., and as we receive by faith the sure pledge of it offered in Christ. Then love is accessory or an inferior aid, a prop to our faith, not a foundation on which it rests. Why then does the Apostle say, We shall assure our hearts before God? He reminds us by these words, that faith does not exist without a good conscience; not that assurance arises from it or depends on it, but that then only we are really and not falsely assured of our union with God, when by the efficacy of his Holy Spirit he manifests himself in our love. For it is ever meet and proper to consider what the Apostle handles; for as he condemns feigned and false profession of faith, he says that a genuine assurance before God we cannot have, except his Spirit produces in us the fruit of love. Nevertheless, though a good conscience cannot be separated from faith, yet no one should hence conclude that we must look to our works in order that our assurance may be certain.

And hereby - Greek, "by this;" that is, by the fact that we have true love to others, and that we manifest it by a readiness to make sacrifices to do them good.
We know that we are of the truth - That we are not deceived in what we profess to be; that is, that we are true Christians. To be of the truth stands opposed to cherishing false and delusive hopes.
And shall assure our hearts before him - Before God, or before the Saviour. In the margin, as in the Greek, the word rendered "shall assure," is "persuade." The Greek word is used as meaning to "persuade," e. g., to the reception and belief of truth; then to persuade anyone who has unkind or prejudiced feelings toward us, or to bring over to kind feelings, "to conciliate," and thus to pacify or quiet. The meaning here seems to be, that we shall in this way allay the doubts and trouble of our minds, and produce a state of quiet and peace, to wit, by the evidence that we are of the truth. Our consciences are often restless and troubled in view of past guilt; but, in thus furnishing the evidence of true piety by love to others, we shall pacify an accusing mind, and conciliate our own hearts, and persuade or convince ourselves that we are truly the children of God. See Robinson, Lexicon, sub voce πείθω peithō, I. b. In other words, though a person's heart may condemn him as guilty, and though he knows that God sees and condemns the sins of his past life, yet the agitations and alarms of his mind may be calmed down and soothed by evidence that he is a child of God, and that he will not be finally condemned. A true Christian does not attempt to conceal the fact that there is much for which his own heart and conscience might justly accuse him but he finds, notwithstanding all this, evidence that he is a child of God, and he is persuaded that all will be well.

Hereby we know that we are of the truth - That we have the true religion of the Lord Jesus, and shall assure our hearts - be persuaded in our consciences, that we have the truth as it is in Jesus; as no man can impose upon himself by imagining he loves when he does not: he may make empty professions to others, but if he loves either God or man, he knows it because he feels it; and love unfelt is not love, it is word or tongue. This the apostle lays down as a test of a man's Christianity, and it is the strongest and most infallible test that can be given. He that loves feels that he does love; and he who feels that he loves God and man has true religion; and he who is careful to show the fruits of this love, in obedience to God and humane acts to man, gives others the fullest proof that he has the loving mind that was in Jesus.

(19) And hereby we know that we are of the truth, (20) and shall assure our hearts before him.
(19) He commends charity, by three effects: for first of all, by it we know that we are indeed the sons of God, as he showed before.
(20) Therefore it comes that we have a quiet conscience, as on the opposite side he that thinks that he has God for a judge, because he is guilty to himself either he is never or else very rarely quiet, for God has a far sharper sight then we, and judges more severely.

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.

hereby--Greek, "herein"; in our loving in deed and in truth (1-John 3:18).
we know--The oldest manuscripts have "we shall know," namely, if we fulfil the command (1-John 3:18).
of the truth--that we are real disciples of, and belonging to, the truth, as it is in Jesus: begotten of God with the word of truth. Having herein the truth radically, we shall be sure not to love merely in word and tongue. (1-John 3:18).
assure--literally, "persuade," namely, so as to cease to condemn us; satisfy the questionings and doubts of our consciences as to whether we be accepted before God or not (compare Matthew 28:14; Acts 12:20, "having made Blastus their friend," literally, "persuaded"). The "heart," as the seat of the feelings, is our inward judge; the conscience, as the witness, acts either as our justifying advocate, or our condemning accuser, before God even now. John 8:9, has "conscience," but the passage is omitted in most old manuscripts. John nowhere else uses the term "conscience." Peter and Paul alone use it.
before him--as in the sight of Him, the omniscient Searcher of hearts. Assurance is designed to be the ordinary experience and privilege of the believer.

Hereby we know, etc. Because our love is active and practical.
Assure our hearts. Have a good conscience.
For if our heart condemn us. If we have a troubled conscience because we have not kept the law of love, God, who is greater and whose condemnation is a far more serious affair, knoweth all things and seeth our failure in duty.
If our heart condemn us not, etc. Then we have a conscience void of offense before God and are assured that he will hear us.
And whatsoever we ask. We can then believe that he will hear our prayers because we are keeping his commandments.

And hereby we know - We have a farther proof by this real, operative love. That we are of the truth - That we have true faith, that we are true children of God. And shall assure our hearts before him - Shall enjoy the assurance of his favour, and the "testimony of a good conscience toward God." The heart, in St. John's language, is the conscience. The word conscience is not found in his writings.