Expositor's Bible Commentary Commentary 1 John 5:10

"He that believeth on the Son of God hath the witness in him: he that believeth not God hath made him a liar; because he hath not believed in the witness that God hath borne concerning his Son." — 1 John 5:10 (ASV)

(10a) Here the fact that the incarnate and crucified Jesus is God’s own Son is clearly set forth. Those who believe this testimony receive the Father’s own witness in their hearts that they are right to trust in Christ. Faith itself is God’s own gift to the believer to lay hold of the Father. “Believing” becomes a “receiving,” and the work of God in Christ results in forgiveness of sins and inward establishment of the love of God. Faith in the Son immediately becomes faith in the Father (cf. 2:23).

(10b) The gravity of receiving this witness is now demonstrated by the corollary: “Anyone who does not believe [the witness borne by] God [about the Son] has made him out to be a liar.” To receive the Son is to receive the Father. To deny the Son is to deny the Father. John, then, cannot allow that one can profess belief in God, as did his opponents, and yet reject God’s own testimony to his Son. Such rejection cannot be excused on the basis of ignorance. Rather, it is deliberate unbelief, the character of which in the end impugns the very being and character of God. If Jesus is not God’s own Son in the flesh, then God is no longer the truth. He is the liar.