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.

By this the love of God was displayed in us, in that God has sent His [One and] only begotten Son [the One who is truly unique, the only One of His kind] into the world so that we might live through Him.

And we [have seen and] know [by personal experience] that the Son of God has [actually] come [to this world], and has given us understanding and insight so that we may [progressively and personally] know Him who is true; and we are in Him who is true—in His Son Jesus Christ. This is the true God and eternal life.

Whoever confesses and acknowledges that Jesus is the Son of God, God abides in him, and he in God.

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.

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.