John’s First Epistle
1 Jno. 5:6-12
This is he who came by water and blood—Jesus Christ; not by the water only but by the water and the blood. And the Spirit is the one who testifies, because the Spirit is the truth. For there are three that testify: the Spirit and the water and the blood; and these three agree. If we receive the testimony of men, the testimony of God is greater, for this is the testimony of God that he has borne concerning his Son. Whoever believes in the Son of God has the testimony in himself. Whoever does not believe God has made him a liar, because he has not believed in the testimony that God has borne concerning his Son. And this is the testimony, that God gave us eternal life, and this life is in his Son. Whoever has the Son has life; whoever does not have the Son of God does not have life. -1 Jno., 5:6-12
John is principally concerned with evidence and testimony that Jesus is the Christ, in the gospel of John. That concern surfaces here in his first epistle. This paragraph is mainly concerned with testimony that is part of the evidence that Jesus is who He claims to be.
The testimony of God has been abundantly given. He has borne witness to His Son, leading John to stress that faith in Him is essential. “Whoever has the son has life; whoever does not have the son of God does not have life.”
“Having” the Son of God means – He is in your heart and life, as real, true and the only way out of sin. God grants eternal life through His Son. Have you, by the activity of faith, accepted that grant?