1 John 5:9-13

If we accept [as we do] the testimony of men [that is, if we are willing to take the sworn statements of fallible humans as evidence], the testimony of God is greater [far more authoritative]; for this is the testimony of God, that He has testified regarding His Son. The one who believes in the Son of God [who adheres to, trusts in, and relies confidently on Him as Savior] has the testimony within himself [because he can speak authoritatively about Christ from his own personal experience]. The one who does not believe God [in this way] has made Him [out to be] a liar, because he has not believed in the evidence that God has given regarding His Son. And the testimony is this: God has given us eternal life [we already possess it], and this life is in His Son [resulting in our spiritual completeness, and eternal companionship with Him]. He who has the Son [by accepting Him as Lord and Savior] has the life [that is eternal]; he who does not have the Son of God [by personal faith] does not have the life. These things I have written to you who believe in the name of the Son of God [which represents all that Jesus Christ is and does], so that you will know [with settled and absolute knowledge] that you [already] have eternal life.