John Calvin Commentary 1 John 5:20

"And we know that the Son of God is come, and hath given us an understanding, that we know him that is true, and we are in him that is true, [even] in his Son Jesus Christ. This is the true God, and eternal life." — 1 John 5:20 (ASV)

And we know that the Son of God is come. As the children of God are assailed on every side, he, as we have said, encourages and exhorts them to persevere in resisting their enemies. He does this because they fight under the banner of God and certainly know that they are ruled by his Spirit. But he now reminds them where this knowledge is especially to be found.

He then says that God has been so made known to us that now there is no reason for doubting. The Apostle does not without reason dwell on this point, for unless our faith is really founded on God, we shall never stand firm in the contest. For this purpose, the Apostle shows that we have obtained through Christ a sure knowledge of the true God, so that we may not fluctuate in uncertainty.

By true God, he does not mean one who tells the truth, but him who is really God; and he calls him so to distinguish him from all idols. Thus, true is in opposition to what is fictitious, for it is ἀληθινὸς, and not ἀληθής. A similar passage is in John:

“This is eternal life, to know thee,
the only true God,
and him whom thou hast sent,
Jesus Christ” (John 17:3).

And he justly ascribes to Christ this office of illuminating our minds as to the knowledge of God. For, as he is the only true image of the invisible God, as he is the only interpreter of the Father, as he is the only guide of life, indeed, as he is the life and light of the world and the truth, as soon as we depart from him, we necessarily become vain in our own devices.

And Christ is said to have given us an understanding, not only because he shows us in the gospel what sort of being is the true God, and also illuminates us by his Spirit, but because in Christ himself we have God manifested in the flesh, as Paul says, since in him dwells all the fullness of the Deity, and are hid all the treasures of knowledge and wisdom (Colossians 2:9). Thus, the face of God, in a manner, appears to us in Christ. This is not to say that there was no knowledge, or only a doubtful knowledge of God, before the coming of Christ, but that now he manifests himself more fully and more clearly. And this is what Paul says in 2 Corinthians 4:6, that

God, who formerly commanded light to shine out of darkness at the creation of the world, hath now shone in our hearts through the brightness of the knowledge of his glory in the face of Christ.

And it must be observed that this gift is peculiar to the elect. Christ, indeed, kindles for all indiscriminately the torch of his gospel; but not all have the eyes of their minds opened to see it. On the contrary, Satan spreads the veil of blindness over many. Then the Apostle means the light which Christ kindles within the hearts of his people, and which, when once kindled, is never extinguished, though in some it may for a time be smothered.

We are in him that is true. By these words, he reminds us how efficacious the knowledge which he mentions is, precisely because by it we are united to Christ and become one with God. For it has a living root, fixed in the heart, by which God lives in us and we in him. As he says, without a copulative, that: we are in him that is true, in his Son, he seems to express the manner of our union with God, as though he had said that we are in God through Christ.

This is the true God. Though the Arians have attempted to elude this passage, and some agree with them to this day, yet we have here a remarkable testimony to the divinity of Christ. The Arians apply this passage to the Father, as though the Apostle would again repeat that he is the true God.

But nothing could be more frigid than such a repetition. It has already twice testified that the true God is he who has been made known to us in Christ; why should he again add, This is the true God? It applies, indeed, most suitably to Christ. For after having taught us that Christ is the guide by whose hand we are led to God, he now, by way of amplifying, affirms that Christ is that God, lest we think that we are to seek further. And he confirms this view by what is added: and eternal life.

Doubtless, the one spoken of as being the true God and eternal life is the same. I pass by this: that the relative οὗτος usually refers to the last person mentioned. I say, then, that Christ is properly called eternal life, and no one can deny that this mode of speaking perpetually occurs in John.

The meaning is that when we have Christ, we enjoy the true and eternal God, for nowhere else is he to be sought. Secondly, we thus become partakers of eternal life, because it is offered to us in Christ, though hidden in the Father. The origin of life is, indeed, the Father, but the fountain from which we are to draw it is Christ.