1 John 5:10 ¹⁰The one who believes in the Son of God has the witness in himself; the one who does not believe God makes him a liar, because he does not believe in the witness which God has witnessed about his Son.

Believing in Jesus is the fulfillment of God’s plan for us. The Holy Spirit draws all people towards Jesus, whether they realize it or not. The reflexive pronoun in himself (en heautō) could refer back to the subject of the sentence: the one who believes. If so, this construction indicates the inner confirmation one can have about the gospel and the identity of Jesus. The Holy Spirit bears witness within our heart, mind, or conscience that Jesus is the truth. A person can have a growing conviction about Jesus as one’s faith and understanding grow.

Internal affirmation is supported by external confirmation from God. John may be referring once again to when the voice of God spoke at Jesus’ baptism or transformation on the mount. As far as Scriptural evidence goes, John was not an eyewitness to Jesus’ baptism but, along with Peter and James, saw Jesus on the mountain. In both situations, a voice from heaven said that the Father was well pleased with the Son. God witnessed to the truth of Jesus in others ways, including the impossible miracles Jesus performed and the powerful words he preached. The greatest witness was Jesus’ resurrection from the dead.

Refusing to believe in Jesus is a rejection of the truth. Believing in Jesus is more than head knowledge or a simple statement that Jesus was a real person who lived at a point in time. This belief must be faith, a trust in Jesus as the atoning sacrifice for sins. This faith requires the affirmation of Jesus’ incarnation as the divine Word from God and his life, death, and resurrection as a human. It requires simple humility that draws us into full commitment and consecration to Jesus as Lord. The Holy Spirit will guide those with simple faith into the depths of this truth. Refusing to believe the gospel is a rejection of God because it denies the truth, doubts God, and says the whole story is made up. John concludes that this essentially makes God a liar.