John 5:37
“And the Father Himself, which has sent Me, has borne witness of Me.”
Where did He “bear witness of” Him? In Jordan: “This is My beloved Son, in whom I am well pleased”; hear Him. Yet even this needed proof. The testimony of John then was clear, for they themselves had sent to him, and could not deny it. The testimony from miracles was in like manner clear, for they had seen them wrought, and had heard from him who was healed, and had believed; whence also they drew their accusation. It therefore remained to give proof to the testimony of the Father. Next in order to effect this, He added,
“You have neither heard His voice at any time”:
How then says Moses, “The Lord spoke, and Moses answered”?; and David, “He had heard a tongue which he knew not”; and Moses again, “Is there any such people which has 'heard the voice of God?'?”
“Nor seen His shape.”
Yet Isaiah, Jeremiah, and Ezekiel, are said to have seen Him, and many others. What then is that which Christ says now? He guides them by degrees to a philosophical doctrine, showing that with God is neither voice nor shape, but that He is higher than such forms or sounds like these. For as when He says, “You have not heard His voice,” He does not mean that God does indeed utter a voice, but one which cannot be heard; so when He says, “Nor seen His shape,” He does not mean that God has a shape though one invisible, but that neither of these things belongs to God. And in order that they might not say, “You are a boaster, God spoke to Moses only”; (this at least they did say, “We know that God spoke with Moses: as for this fellow, we know not whence He is”) on this account He spoke as He did, to show that there is neither voice nor shape with God. “But why,” He says, “name I these things? Not only have ye 'neither heard His voice nor seen His shape,' but it is not even in your power to assert that of which you most boast and of which you are all most fully assured, namely, that you have received and keep His commandments.” Wherefore He adds,
Source: Homilies on the Gospel of John (New Advent)