John 5:32

First then checking their disputatious spirit by setting forth what they would say, and showing that He knew the secrets of their hearts, and giving this first proof of His power, after stating the objection He supplieth other proofs clear and indisputable, producing three witnesses to what He said, namely, the works wrought by Him, the witness of the Father, and the preaching of John. And He putteth first the less important witness of John. For after saying, "There is another that beareth witness of Me, and I know that his witness is true," He addeth, "Ye sent unto John, and he bare witness unto the truth." Yet if Thy witness be not true, how sayest Thou, "I know that the testimony of John is true, and that he hath borne witness to the truth"? and seest thou (O man) how clear it hence is, that the expression, "My witness is not true," was addressed to their secret thoughts? "What then," saith some one, "if John bare witness partially." That the Jews might not assert this, see how He removeth this suspicion. For He said not, "John testified of Me," but, "Ye first sent to John, and ye would not have sent had ye not deemed him trustworthy." Nay, what is more, they had sent not to ask him about Christ, but about himself, and the man whom they deemed trustworthy in what related to himself they would much more deem so in what related to another. For it is, so to speak, the nature of us all not to give so much credit to those who speak of themselves as to those who speak of others; yet him they deemed so trustworthy as not to require even concerning himself any other testimony. For they who were sent said not, "What sayest thou concerning Christ?" but, "Who art thou? What sayest thou of thyself?" So great admiration felt they for the man. Now to all this Christ made allusion by saying, "Ye sent unto John." And on this account the Evangelist hath not merely related that they sent, but is exact as to the persons sent that they were Priests and of the Pharisees, not common or abject persons, nor such as might be corrupted or cheated, but men able to understand exactly what he said.

In answer then, he puts forth three clear and irrefragable proofs, three witnesses as it were, to the truth of what He had said; the works which He had done, the testimony of the Father, and the preaching of John: putting the least of these foremost, i. e. the preaching of John: There is another that beareth witness of Me: and I know that the witness which he witnesseth of Me is true.

(de Verb. Dom. s. 43) He knew Himself that His witness of Himself was true, but in compassion to the weak and unbelieving, the Sun sought for candles, that their weak sight might not be dazzled by His full blaze. And therefore John was brought forward to give his testimony to the truth. Not that there is such testimony really, for whatever witnesses bear witness to Him, it is really He who bears witness to Himself; as it is His dwelling in the witnesses, which moves them so to give their witness to the truth.

Or thus; Christ, being both God and man, He shows the proper existence of both, by sometimes speaking according to the nature he took from man, sometimes according to the majesty of the Godhead. If I bear witness of Myself, My witness is not true: this is to be understood of His humanity; the sense being, If I, a man, bear witness of Myself, i. e. without God, My witness is not true: and then follows, There is another that beareth witness of Me. The Father bore witness of Christ, by the voice which was heard at the baptism, and at the transfiguration on the mount. And I know that His witness is true; because He is the God of truth. How then can His witness be otherwise than true?