“He who believes in the Son of God has the witness in himself; he who does not believe God has made Him a liar, because he has not believed the testimony that God has given of His Son.”
he who does not believe God
This phrase introduces the alternative to the faith of the previous phrase. John writes against the Gnostics. Gnostics believed that Jesus was an ordinary human at His birth but became the Messiah at His baptism. According to them, Jesus received deity from His baptism until just before the cross when the Spirit left Him.
has made Him a liar,
Anyone who does not believe what God says in the Word makes God a liar. In verses 9-12, God gives testimony to Jesus Christ as the Son of God. Anyone who rejects Jesus as the Son makes God a liar. He brands God a liar. It is one thing to call God a liar but it is another thing to “make” Him a liar.
1: 10 “If we say that we have not sinned, we make Him a liar, and His word is not in us.”
Assurance of salvation rests on God’s promise of salvation confirmed in His Word.
Making God a liar is worse than calling God a liar. If you call a person a liar, you get into trouble, but there is no way for you to make a person a liar. The person who does not believe God brands God a liar, “because he believeth not the record, that God gave of His Son.”
The Bible is God’s record. We must believe the record that God gave concerning Jesus in order to go to heaven. That is the essential, irreducible minimum to be right with God.
Are you greatly exercised about the assurance of your salvation? We do not gain assurance of salvation by feeling, but by trust in God’s record of how we become Christians. It is an issue of believing the trustworthiness of God’s Word. Note the next verse:
5: 11 “And this is the testimony: that God has given us eternal life, and this life is in His Son.”