John Calvin Commentary John 5:31

"If I bear witness of myself, my witness is not true." — John 5:31 (ASV)

If I testify concerning myself. He does not here take anything away from the credit due to His testimony, which He elsewhere asserts in strong terms, but He speaks by way of concession. For Christ, having been in other respects most abundantly supported, consents that they need not believe His word. “If My testimony concerning Myself,” He says, “is suspected by you according to ordinary human custom, let it count for nothing.” Now, we know that what anyone asserts about himself is not generally considered true and authentic, although in other respects he speaks the truth, because no one is a competent witness in his own case. Though it would be unjust to reduce the Son of God to this rank, yet He prefers to surrender His right, so that He may convince His enemies by the authority of God.