3. 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.)

4. He that saith, I know him. How does he prove that they are liars who boast that they have faith without piety? even by the contrary effect; for he has already said, that the knowledge of God is efficacious. For God is not known by a naked imagination, since he reveals himself inwardly to our hearts by the Spirit. Besides, as many hypocrites vainly boast that they have faith, the Apostle charges all such with falsehood; for what he says would be superfluous, were there no false and vain profession of Christianity made by man.

5. But whoso keepeth. He now defines what a true keeping of God's law is, even to love God. This passage is, I think, incorrectly explained by those who understand that they please the true God who keep his word. Rather take this as its meaning, "to love God in sincerity of heart, is to keep his commandments." For he intended, as I have before reminded you, briefly to shew what God requires from us, and what is the holiness of the faithful. Moses also said the same thing, when he stated the sum of the law.

"Now, O Israel, what does the Lord require of thee, but to fear and love him, and to walk in his precepts?"
(Deuteronomy 10:12.)

And again he says,

"Choose life, even to love the Lord thy God, to serve him and to cleave to him." (Deuteronomy 30:19, 20)

For the law, which is spiritual, does not command only external works, but enjoins this especially, to love God with the whole heart.

That no mention is here made of what is due to men, ought not to be viewed as unreasonable; for brotherly love flows immediately from the love of God, as we shall hereafter see. Whosoever, then, desires that his life should be approved by God, must have all his doings directed to this end. If any one objects and says, that no one has ever been found who loved God thus perfectly; to this I reply, that it is sufficient, provided every one aspired to this perfection according to the measure of grace given unto him. In the meantime, the definition is, that the perfect love of God is the complete keeping of his law. To make progress in this as in knowledge, is what we ought to do.

Hereby know we that we are in him. He refers to that fruit of the gospel which he had mentioned, even fellowship with the Father and the Son; and he thus confirms the former sentence, by stating what follows, as a consequence. For if it be the end of the gospel to hold communion with God, and no communion can be without love, then no one makes a real progress in faith except he who cleaves from the heart to God.

6. He that saith he abideth in him. As he has before set before us God as light for an example, he now calls us also to Christ, that we may imitate him. Yet he does not simply exhort us to imitate Christ; but from the union we have with him, he proves that we ought to be like him. A likeness in life and deeds, he says, will prove that we abide in Christ. But from these words he passes on to the next clause, which he immediately adds respecting love to the brethren.