John 5:37

37.And the Father who hath sent me. To limit this statement, as some have done, (108) to the voice which was heard at his baptism, (Matthew 3:17,) is a mistake; for he says in the past tense, that the Father ( μεμαρτύρηκε)testified, in order to show that he did not come forward as an unknown person, because the Father had long ago distinguished him by such peculiar marks that, bringing them along with him, he might be recognized. I explain, therefore, that God testified concerning his Son, whenever in past times he held out to the ancient people the hope of salvation, or promised that the kingdom of Israel would be fully restored. In this manner the Jews must have formed an idea of Christ from the Prophets, before he was manifested in the flesh. When having him before their eyes, they despise and therefore reject him, they show plainly that they have no relish for the Law, with which Christ also reproaches them; and yet they boasted of their knowledge of the Law, as if they had been brought up in the bosom of God.

You have never heard his voice. After having complained that they do not receive him, Christ breaks out in still more severe language against their blindness. When he says that they had never heard the voice of God, or seen his shape, these are metaphorical expressions, by which he intends to state generally that they are utterly estranged from the knowledge of God. For as men are made known by the countenance and speech, so God utters his voice to us by the voice of the Prophets, and, in the sacraments, takes, as it were, a visible form, from which he may be known by us according to our feeble capacity. But he who does not recognize God in his lively image, plainly shows by this very fact that he worships no Deity but what he has himself contrived. For this reason Paul says, that the Jews had a vail placed before their eyes, that they might not perceive the glory of God in the face of Christ, (2 Corinthians 3:14.)