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.