If I testify concerning myself. He does not here take any thing 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 should not believe his word. "If my testimony concerning myself," says he, "is suspected by you according to the ordinary custom of men, let it go for nothing." Now we know that what any man asserts about himself is not reckoned to be true and authentic, although in other respects he speak truth, because no man is a competent witness in his own cause. Though it would be unjust to reduce the Son of God to this rank, yet he prefers to surrender his right, that he may convince his enemies by the authority of God.

If I bear witness of myself - If I have no other evidence than my own testimony about myself.
My witness - My testimony; my evidence. The proof would not be decisive.
Is not true - The word "true," here, means worthy of belief, or established by suitable evidence. See Matthew 22:16; "We Know that thou art true" - that is, worthy of confidence, or that thou hast been truly sent from God, Luke 20:21; John 8:13, John 8:17. The law did not admit a man to testify in his own case, but required two witnesses, Deuteronomy 17:6. Though what Jesus said was true John 8:13, John 8:17, yet he admitted it was not sufficient testimony alone to claim their belief. They had a right to expect that his statement that he came from God would be confirmed by other evidence. This evidence he gave in the miracles which he performed as proof that God had sent him.

If I bear witness - If I had no proof to bring of my being the Messiah, and equal to God, common sense would direct you to reject my testimony; but the mighty power of God, by which I work my miracles, sufficiently attests that my pretensions are well founded.
Bishop Pearce gives a different turn to this verse, by translating it interrogatively, thus: "If I only bear witness of myself, is not my witness true? i.e. is it, on that account, not true? In John 8:14, he says, Though I bear record of myself, yet my record is true. And in John 8:18, he says, I am one that bear witness of myself."

If I bear witness of myself, my witness is not (p) true.
(p) Faithful, that is, worthy to be credited; see (John 8:14).

If I bear witness of myself,.... Which was not allowed any man to do; nor indeed is it proper that a man should be a witness in his own cause: and, according to the Jewish canons, a man might not be a witness for his wife, because she was reckoned as himself.
"An husband is not to be believed in bearing witness for his wife, that had been carried captive, that she is not defiled, , "for no man witness of himself" (k).''
So likewise they say (l),
"a city that is subdued by an army, all the priestesses (or priests' daughters) that are found in it are rejected (from the priesthood, as defiled); but if they have witnesses, whether a servant, or an handmaid, lo, they are to be believed; but no man is to be believed for himself: says R. Zechariah ben Hakatzah, by this habitation (swearing by the temple) her hand was not removed from my hand, from the time the Gentiles entered Jerusalem, till they went out: they replied to him, "no man bears witness of himself".''
Christ reasons here upon their own principles, and according to their sense of things, that should he bear witness of himself; then, says he,
my witness is not true, , not to be believed, or admitted as an authentic testimony: and so the Ethiopic version renders it, "is not credible"; not valid in law, or in such a court of judicature in which Christ now was; for, as according to the Jewish law, no man was admitted a witness for himself, so neither was anything established by a single testimony, but by the mouth of two or three witnesses, Deuteronomy 19:15. Christ's meaning is, that his testimony alone, his single witness, how true soever it was, would stand for nothing in their court; and therefore he would not insist upon it, but drop it; for "true" here, is not opposed to that which is "false", but to that which is not valid in law. Christ's testimony was true in itself; nor could it be any other, it coming from him, who is truth itself, the "Amen", and faithful witness; but being considered as an human testimony, and in his own cause, was not to be admitted as sufficient; and this he allows. From arguments, proving his equality with the Father, he passes to testimonies; and without ranking use of his own, he had enough to produce, and which were valid and authentic, and are as follow.
(k) Maimon. Issure Bia, c. 18. sect. 19. (l) Misn. Cetubot, c. 2. sect. 9. T. Bab. Cetubot, fol. 27. 2. Juchasin, fol. 56. 1.

If I . . . witness of myself--standing alone, and setting up any separate interest.

If I testify of myself - That is, if I alone, (which indeed is impossible,) my testimony is not valid.