“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.”
because he has not believed
“Believed the testimony” expresses personal trust and reliance on the Son and His ministry on our behalf. This is more than believing the fact that He is the Son; it is relying on or resting in what God said about His Son. We honor God when we trust Him. God puts belief and unbelief in stark contrast.
John combines the two words “believe” and “in” for the second time in this verse. Christians put their trust or reliance in the Father’s “testimony” about the Son. Disbelief assaults the character of the person disbelieved. This is not simply believing a person but believing in a person.
God gave His testimony in verses 8 and 9. The purpose of God’s testimony is to offer faith in His Son (Jn 1:7; 20:31). “Testimony” is the cause of trust in the Son.
Failure to believe in Jesus, the Son of God, is a two-fold failure: 1) failure to trust in Christ for salvation and 2) failure to believe in God as a credible witness. Unbelief makes God out to be a liar. The person who believes God credits His witness.
Note the change of parallelism here. It is not trust in Christ or even God but rather simply believing what God has to say. We must believe what God says about Christ before we can believe in the Son of God Himself. Faith comes by hearing and hearing by the Word of God. We cannot separate the Son and the witness about the Son.
We credit God’s witness to truth when we believe.
We do not determine whether we are Christians by how we feel. We will never gain assurance of salvation by emotions. We gain assurance by accepting God’s Word as true. It is the objective Word of God and not our subjective experience that gives us assurance of salvation.
Ro 10: 17 “So then faith comes by hearing, and hearing by the word of God.”