And hereby, or by this. After having treated of the doctrine respecting the gratuitous remission of sins, he comes to the exhortations which belong to it, and which depend on it. And first indeed he reminds us that the knowledge of God, derived from the gospel, is not ineffectual, but that obedience proceeds from it. He then shews what God especially requires from us, what is the chief thing in life, even love to God. What we read here of the living knowledge of God, the Scripture does not without reason repeat everywhere; for nothing is more common in the world than to draw the doctrine of religion to frigid speculations. In this way theology has been adulterated by the Sorbonian sophists, so that from their whole science not even the least spark of true religion shines forth. And curious men do everywhere learn so much from God's word, as enables them to prattle for the sake of display. In short, no evil has been more common in all ages than vainly to profess God's name. John then takes this principle as granted, that the knowledge of God is efficacious. He hence concludes, that they by no means know God who keep not his precepts or commandments. Plato, though groping in darkness, yet denied that "the beautiful" which he imagined, could be known, without filling man with the admiration of itself; so he says in his Phaedrus and in other places. How then is it possible for thee to know God, and to be moved by no feeling? Nor does it indeed proceed only from God's nature, that to know him is immediately to love him; but the Spirit also, who illuminates our minds, inspires our hearts with a feeling conformable to our knowledge. At the same time the knowledge of God leads us to fear him and to love him. For we cannot know him as Lord and Father, as he shews himself, without being dutiful children and obedient servants. In short, the doctrine of the gospel is a lively mirror in which we contemplate the image of God, and are transformed into the same, as Paul teaches us in 2-Corinthians 3:18. Where, therefore, there is no pure conscience, nothing can be there but an empty phantom of knowledge. We must notice the order when he says, We do know that we know him; for he intimates that obedience is so connected with knowledge, that the last is yet in order the first, as the cause is necessarily before its effect. If we keep his commandments But there is no one who in everything keeps them; there would thus be no knowledge of God in the world. To this I answer, that the Apostle is by no means inconsistent with himself; since he has before shewed that all are guilty before God, he does not understand that those who keep his commandments wholly satisfy the law (no such example can be found in the world;) but that they are such as strive, according to the capacity of human infirmity, to form their life in conformity to the will of God. For whenever Scripture speaks of the righteousness of the faithful, it does not exclude the remission of sins, but on the contrary, begins with it. But we are not hence to conclude that faith recumbs on works; for though every one receives a testimony to his faith from his works, yet it does not follow that it is founded on them, since they are added as an evidence. Then the certainty of faith depends on the grace of Christ alone; but piety and holiness of life distinguish true faith from that knowledge of God which is fictitious and dead; for the truth is, that those who are in Christ, as Paul says, have put off the old man. (Colossians 3:9.)

And hereby we do know that we know him - To wit, by that which follows, we have evidence that we are truly acquainted with him, and with the requirements of his religion; that is, that we are truly his friends. The word "him" in this verse, seems to refer to the Saviour. On the meaning of the word "know," see the notes at John 17:3. The apostle had stated in the previous part of this Epistle some of the leading points revealed by the Christian religion, and he here enters on the consideration of the nature of the evidence required to show that we are personally interested in it, or that we are true Christians. A large part of the Epistle is occupied with this subject. The first, the grand evidence - that without which all others would be vain - he says is, that we keep his commandments.
If we keep his commandments - See the notes at John 14:15. Compare John 14:23-24; John 15:10, John 15:14.

And hereby we do know that we know him - If we keep the commandments of God, loving him with all our heart, and our neighbor as ourselves, we have the fullest proof that we have the true saving knowledge of God and his Christ. The Gnostics pretended to much knowledge, but their knowledge left them in possession of all their bad passions and unholy habits; they, therefore, gave no proof that they had known either God or his Son Jesus - nor is any man properly acquainted with God, who is still under the power of his sins.

(2) And hereby we do know that we (e) know him, (e) if we keep his commandments.
(2) He returns to the testimony of our union with God, that is, to sanctification, declaring what it is to walk in the light, that is, to keep God's commandments. By this it follows that holiness does not consist in those things which men have devised, neither in a vain profession of the gospel.
(d) This must be understood of such a knowledge as has faith with it, and not of a common knowledge.
(e) For the tree is known by the fruit.

And hereby we do know that we know him,.... Either the Father, with whom Christ is an advocate; not as the God of nature, and by the light of it, nor as the lawgiver and Judge of the whole earth, and by the law of Moses; but as the God of all grace, as a God pardoning iniquity, transgression, and sin, as the Father of Christ, and as in him by the Gospel; and this not in a mere notional and speculative way, but with love and affection; not with fear and trembling, as devils know him, nor in theory, as formal professors and hypocrites, but with a knowledge, joined with hearty love of him, and cheerful obedience to him: or else Christ, the advocate and propitiation for sin; and him also, not with a mere notional knowledge of his person and offices, which carnal men and devils themselves have of him, but with that which is spiritual, special, and saving, being from the Spirit and grace of God; and regards Christ as a Saviour, as a propitiatory sacrifice for sin, and an advocate with God the Father; and by which he is approved as such, to the rejection of all other savours, sacrifices, and advocates; and is trusted, confided, and believed in as such, and affectionately loved, and that above all others, in sincerity and truth; and is readily obeyed in his word and ordinances; for where there is true knowledge of Christ, there is faith in him; and where there is faith in him, there is love to him, for faith works by love; and where there is love to him, there will be an observance of his commands; and this is here made the evidence of the true knowledge of him: for it follows,
if we keep his commandments; not the commandments of men, for the keeping of them arises from ignorance of God, and is a proof of it; nor the commandments of the ceremonial law, which are abolished, particularly circumcision, which is opposed to the keeping of the commandments of God, 1-Corinthians 7:19; but either those of the moral law, and which are more particularly the commandments of God the Father; the observance of which, though it cannot be with perfection, yet being in faith, and from love to God, and with a view to his glory, is an evidence of the true knowledge of him and of his will: or else those commandments, which are more especially the commandments of Christ Jesus; such as the ordinances of baptism and the Lord's supper, which are peculiar to the Gospel dispensation; and which being kept as they were delivered by Christ, and in his name and strength, and to his glory, without depending on them for life and salvation, is an argument and proof of the right knowledge of him; and particularly his new commandment of loving one another may be chiefly designed, that being what the apostle has greatly in view throughout this epistle; now let it be observed, that keeping of the commands of God, or Christ, is not the knowledge of either of them itself, for much may be done in an external way, yet neither God nor Christ be spiritually and savingly known; nor is it the cause of such knowledge, for that is owing to the Spirit and grace of God; but is an effect or consequence of spiritual knowledge, and so an evidence of it; hereby is not the knowledge itself, but the knowledge of that knowledge, that is, that it is true and genuine.

What knowledge of Christ can that be, which sees not that he is most worthy of our entire obedience? And a disobedient life shows there is neither religion nor honesty in the professor. The love of God is perfected in him that keeps his commandments. God's grace in him attains its true mark, and produces its sovereign effect as far as may be in this world, and this is man's regeneration; though never absolutely perfect here. Yet this observing Christ's commands, has holiness and excellency which, if universal, would make the earth resemble heaven itself. The command to love one another had been in force from the beginning of the world; but it might be called a new command as given to Christians. It was new in them, as their situation was new in respect of its motives, rules, and obligations. And those who walk in hatred and enmity to believers, remain in a dark state. Christian love teaches us to value our brother's soul, and to dread every thing hurtful to his purity and peace. Where spiritual darkness dwells, in mind, the judgment, and the conscience will be darkened, and will mistake the way to heavenly life. These things demand serious self-examination; and earnest prayer, that God would show us what we are, and whither we are going.

hereby--Greek, "in this." "It is herein," and herein only, that we know (present tense) that we have knowledge of (perfect tense, once-for-all obtained and continuing knowledge of) Him" (1-John 2:4, 1-John 2:13-14). Tokens whereby to discern grace are frequently given in this Epistle. The Gnostics, by the Spirit's prescient forewarning, are refuted, who boasted of knowledge, but set aside obedience. "Know Him," namely, as "the righteous" (1-John 2:1, 1-John 2:29); our "Advocate and Intercessor."
keep--John's favorite word, instead of "do," literally, "watch," "guard," and "keep safe" as a precious thing; observing so as to keep. So Christ Himself. Not faultless conformity, but hearty acceptance of, and willing subjection to, God's whole revealed will, is meant.
commandments--injunctions of faith, love, and obedience. John never uses "the law" to express the rule of Christian obedience: he uses it as the Mosaic law.

And hereby we do know that we know him. The evidences that we have a saving knowledge of Christ is loyal obedience to his commandments.
He that saith, etc. If one claims to have a saving knowledge of Christ, yet lives in disobedience, his life puts the lie to his words.
But whoso keepeth his word, etc. It is by keeping his commandments that the love of God is made perfect in us. Obedience is the result and proof of love, and also gives love the opportunity to flow over the whole life. Compare John 14:21.
Hereby. By our loyal obedience.
He that saith he abideth in him. Who so abideth in Christ, and lives by the life Christ imparts, must show that life by a life like that of Christ. See John 15:4.

And hereby we know that we truly and savingly know him - As he is the advocate, the righteous, the propitiation. If we keep his commandments - Particularly those of faith and love.