1 John 5:20

20And 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, and for this reason, 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 except our faith is really founded on God, we shall never stand firm in the contest. For this purpose the Apostle shews 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 so calls him to distinguishing 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, yea, 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 shews 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 it is that the face of God in a manner appears to us in Christ; not that there was no knowledge, or 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 all have not the eyes of their minds opened to see it, but on the contrary Satan spreads the veil of blindness over many. Then the Apostle means the light which Christ kindles within in 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 is that knowledge which he mentions, even 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 it comes that 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. (97)

This is the true God Though the Arians have attempted to elude this passage, and some agree with them at 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 should 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 should think that we are to seek further; and he confirms this view by what is added, and eternal life. It is doubtless the same that is spoken of, as being the true God and eternal life. I pass by this, that the relative οὗτος usually refers to the last person. I say, then, that Christ is properly called eternal life; and that this mode of speaking perpetually occurs in John, no one can deny.

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