And we know that the Son of God is come, and hath given us an understanding, that we may know him that is true, and we are in him that is true, even in his Son Jesus Christ. This is the true {m} God, and eternal life.

(m) The divinity of Christ is most clearly proved by this passage.

People's New Testament

5:20 And we know that the Son of God is come. Not only by testimony from men but by God's witness. We have life in Christ, and Christ dwells in us.

This is the true God, and eternal life. In Christ the true God is revealed to us, and in him we have eternal life.

Wesley's Notes

5:20 And we know - By all these infallible proofs. That the Son of God is come - Into the world. And he hath given us a spiritual understanding, that we may know him, the true one - The faithful and true witness. And we are in the true one - As branches in the vine, even in Jesus Christ, the eternal Son of God. This Jesus is the only living and true God, together with the father and the Spirit, and the original fountain of eternal life. So the beginning and the end of the epistle agree.

Jamieson-Fausset-Brown Bible Commentary

20. Summary of our Christian privileges.

is come-is present, having come. "He is here-all is full of Him-His incarnation, work, and abiding presence, is to us a living fact" [Alford].

given us an understanding-Christ's, office is to give the inner spiritual understanding to discern the things of God.

that we may know-Some oldest manuscripts read, "(so) that we know."

him that is true-God, as opposed to every kind of idol or false god (1Jo 5:21). Jesus, by virtue of His oneness with God, is also "He that is true" (Re 3:7).

even-"we are in the true" God, by virtue of being "in His Son Jesus Christ."

This is the true God-"This Jesus Christ (the last-named Person) is the true God" (identifying Him thus with the Father in His attribute, "the only true God," Joh 17:3, primarily attributed to the Father).

and eternal life-predicated of the Son of God; Alford wrongly says, He was the life, but not eternal life. The Father is indeed eternal life as its source, but the Son also is that eternal life manifested, as the very passage (1Jo 1:2) which Alford quotes, proves against him. Compare also 1Jo 5:11, 13. Plainly it is as the Mediator of ETERNAL LIFE to us that Christ is here contemplated. The Greek is, "The true God and eternal life is this" Jesus Christ, that is, In believing in Him we believe in the true God, and have eternal life. The Son is called "He that is TRUE," Re 3:7, as here. This naturally prepares the way for warning against false gods (1Jo 5:21). Jesus Christ is the only "express image of God's person" which is sanctioned, the only true visible manifestation of God. All other representations of God are forbidden as idols. Thus the Epistle closes as it began (1Jo 1:1, 2).

Matthew Henry's Concise Commentary

5:18-21 All mankind are divided into two parties or dominions; that which belongs to God, and that which belongs to the wicked one. True believers belong to God: they are of God, and from him, and to him, and for him; while the rest, by far the greater number, are in the power of the wicked one; they do his works, and support his cause. This general declaration includes all unbelievers, whatever their profession, station, or situation, or by whatever name they may be called. The Son leads believers to the Father, and they are in the love and favour of both; in union with both, by the indwelling and working of the Holy Spirit. Happy are those to whom it is given to know that the Son of God is come, and to have a heart to trust in and rely on him that is true! May this be our privilege; we shall thus be kept from all idols and false doctrines, and from the idolatrous love of worldly objects, and be kept by the power of God, through faith, unto eternal salvation. To this living and true God, be glory and dominion for ever and ever. Amen.

Matthew Henry's Whole Bible Commentary

Verses 18-21

Here we have,

I. A recapitulation of the privileges and advantages of sound Christian believers. 1. They are secured against sin, against the fulness of its dominion or the fulness of its guilt: We know that whosoever is born of God (and the believer in Christ is born of God, v. 1) sinneth not (v. 18), sinneth not with that fulness of heart and spirit that the unregenerate do (as was said ch. 3:6, 9), and consequently not with that fulness of guilt that attends the sins of others; and so he is secured against that sin which is unavoidably unto death, or which infallibly binds the sinner over unto the wages of eternal death; the new nature, and the inhabitation of the divine Spirit thereby, prevent the admission of such unpardonable sin. 2. They are fortified against the devil's destructive attempts: He that is begotten of God keepeth himself, that is, is enabled to guard himself, and the wicked one toucheth him not (v. 18), that is, that the wicked one may not touch him, namely, to death. It seems not to be barely a narration of the duty or the practice of the regenerate; but an indication of their power by virtue of their regeneration. They are thereby prepared and principled against the fatal touches, the sting, of the wicked one; he touches not their souls, to infuse his venom there a he does in others, or to expel that regenerative principle which is an antidote to his poison, or to induce them to that sin which by the gospel constitution conveys an indissoluble obligation to eternal death. He may prevail too far with them, to draw them to some acts of sin; but it seems to be the design of the apostle to assert that their regeneration secures them from such assaults of the devil as will bring them into the same case and actual condemnation with the devil. 3. they are on God's side and interest, in opposition to the state of the world: And we know that we are of God, and the whole world lieth in wickedness, v. 19. Mankind are divided into two great parties of dominions, that which belongs to God and that which belongs to wickedness or to the wicked one. The Christian believers belong to God. They are of God, and from him, and to him, and for him. They succeed into the right and room of the ancient Israel of God, of whom it is said, The Lord's people is his portion, his estate in this world; Jacob is the lot of his inheritance, the dividend that has fallen to him by the lot of his own determination (Deu. 32:9); while, on the contrary, the whole world, the rest, being by far the major part, lieth in wickedness, in the jaws in the bowels of the wicked one. There are, indeed, were we to consider the individuals, many wicked ones, many wicked spirits, in the heavenly or the ethereal places; but they are united in wicked nature, policy, and principle, and they are united also in one head. there is the prince of the devils and of the diabolical kingdom. There is a head of the malignity and of the malignant world; and he has such sway here that he is called the god of this world. Strange that such a knowing spirit should be so implacably incensed against the Almighty and all his interests, when he cannot but know that it must end in his own overthrow and everlasting damnation! How tremendous is the judgment of God upon that wicked one! May the God of the Christian world continually demolish his dominion in this world, and translate souls into the kingdom of his dear Son! 4. They are enlightened in the knowledge of the true eternal God: "And we know that the Son of God has come, and has given as an understanding, that we may know him that is true, v. 20. The Son of God has come into our world, and we have seen him, and know him by all the evidence that has already been asserted; he has revealed unto us the true God (as Jn. 1:18), and he has opened our minds too to understand that revelation, given us an internal light in our understandings, whereby we may discern the glories of the true God; and we are assured that it is the true God that he hath discovered to us. He is infinitely superior in purity, power, and perfection, to all the gods of the Gentiles. He has all the excellences, beauties, and riches, of the living and true God. It is the same God that, according to Moses's account, made the heavens and the earth, the same who took our fathers and patriarchs into peculiar covenant with himself, the same who brought our ancestors out of Egypt, who gave us the fiery law upon mount Sinai, who gave us his holy oracles, promised the call and conversion of the Gentiles. By his counsels and works, by his love and grace, by his terrors and judgments, we know that he, and he alone, in the fulness of his being, is the living and true God." It is a great happiness to know the true God, to know him in Christ; it is eternal lie, Jn. 17:3. It is the glory of the Christian revelation that it gives the best account of the true God, and administers the best eye-salve for our discerning the living and true God. 5. They have a happy union with God and his Son: "And we are in him that is true, even (or and) in his Son Jesus Christ, v. 20. The Son leads us to the Father, and we are in both, in the love and favour of both, in covenant and federal alliance with both, in spiritual conjunction with both by the inhabitation and operation of their Spirit: and, that you may know how great a dignity and felicity this is, you must remember that this true one is the true God and eternal life" or rather (as it should seem a more natural construction), "This same Son of God is himself also the true God and eternal life" (Jn. 1:1, and here, ch. 1:2), "so that in union with either, much more with both, we are united to the true God and eternal life." Then we have,

II. The apostle's concluding monition: "Little children" (dear children, as it has been interpreted), "keep yourselves from idols, v. 21. Since you know the true God, and are in him, let your light and love guard you against all that is advanced in opposition to him, or competition with him. Flee from the false gods of the heathen world. They are not comparable to the God whose you are and whom you serve. Adore not your God by statues and images, which share in his worship. Your God is an incomprehensible Spirit, and is disgraced by such sordid representations. Hold no communion with your heathen neighbours in their idolatrous worship. Your God is jealous, and would have you come out, and be separated from among them; mortify the flesh, and be crucified to the world, that they may not usurp the throne of dominion in the heart, which is due only to God. The God whom you have known is he who made you, who redeemed you by his Son, who has sent his gospel to you, who has pardoned your sins, begotten you unto himself by his Spirit, and given you eternal life. Cleave to him in faith, and love, and constant obedience, in opposition to all things that would alienate your mind and heart from God. To this living and true God be glory and dominion for ever and ever. Amen."