Expositor's Bible Commentary 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)

John’s third and final affirmation is in fact the summary of the letter. It affirms the point of dispute with the false teachers. Christian faith has to do with Jesus Christ. He is the “Word of life” (1:1), “the eternal life” (v.2), which was with the Father and through the Incarnation came into human history. By his coming, we can know the true God and have fellowship with him. But the false teachers said that this relationship was apart from the Son. Fellowship with God as they taught it came through divine “knowledge” of the subject. From the beginning John denied this teaching. The reality of God can be known only through apprehending the reality that is in the Son. This comes through revelation that is grounded in the facts of history. It requires that we know Jesus Christ as God’s Son and that we live our lives entirely in him. We know by this experiential life in the Son that we are also in the Father and that the Son is indeed the true God, the author of eternal life.

“He” in v.20b is translates “this one”; grammatically it most naturally refers to Jesus Christ (though some refer it to God as “him who is true”). Here at the climax of the letter John ascribes full deity to Jesus. After all, this is the crux of his argument and the basis for his statement that he who is in Jesus is in the Father. For Jesus Christ as the author of eternal life, see v.11; also Jn 11:25; 14:6.