God’s Testimony about His Son
John reasons that God's testimony must be received with greater seriousness than ordinary human testimony, because it comes from God Himself and concerns His Son. The believer possesses this testimony inwardly, while the unbeliever insults God by treating His testimony as false. John then states the content plainly: God has given eternal life, and this life is located in His Son. To have the Son is to have life; to reject the Son is to remain without life. The paragraph brings the whole letter's concern for assurance into sharp Christ-centered focus.
E9ven if we accept human testimony, the testimony of God is greater. For this is the testimony that God has given about His Son. 10Whoever believes in the Son of God has this testimony within him; whoever does not believe God has made Him out to be a liar, because he has not believed in the testimony that God has given about His Son. 11And this is that testimony: God has given us eternal life, and this life is in His Son. 12Whoever has the Son has life; whoever does not have the Son of God does not have life.