Galatians 6:3

“For some time ago Theudas rose up, claiming to be somebody, and a group of about four hundred men joined up with him. But he was killed, and all who were following him were dispersed and came to nothing.

Let no man deceive himself. If any man among you thinks that he is wise in this age, he must become foolish, so that he may become wise.

But from those who were of high reputation (what they were makes no difference to me; God shows no partiality)—well, those who were of reputation contributed nothing to me.

and recognizing the grace that had been given to me, James and Cephas and John, who were reputed to be pillars, gave to me and Barnabas the right hand of fellowship, so that we might go to the Gentiles and they to the circumcised.

The one who believes in the Son of God has this witness in himself. The one who does not believe God has made Him a liar, because he has not believed in the witness which God has borne witness about His Son.