Many people go around saying they believe in God, but they reject and do not believe in the Lord Jesus Christ found in the Bible. The Apostle John in his first epistle makes it very clear concerning this matter. In 1John 5:10 LITV, he wrote, 'The one believing in the Son of God has the witness in himself. The one not believing God has made Him a liar, because he has not believed in the witness which God has witnessed concerning His Son.'
Notice the apostle wrote, 'The one not believing God has made Him a liar, because he has not believed in the witness which God has witnessed concerning His Son.'
The Bible says, 'The one not believing God has made Him a liar.' When a person does not believe the witness that God has given about His Son, that person is calling God a liar. Think about this: If someone calls somebody else a liar, he or she obviously does not believe what that person is telling them. It would be a contradiction in terms to say, 'I believe in God, but I do not believe the witness that God has given about His Son.' If a person does not believe in the Son, then that person is literally saying, 'I do not believe (trust) in God but reject Him.' To reject and not put your faith in the Lord Jesus Christ of the Bible and not trust in Him alone to save you by His death, burial and resurrection, means to reject God, and call Him a liar!
