Augustine of Hippo — as excerpted in the Catena Aurea on John 12:37-43

“(Tr. liii. 11) And be converted, and I should heal them. Is not to be understood here, from the beginning of the sentence—that they should not see with their eyes, nor understand with their hearts, nor be converted; conversion being the free gift of God? ord, shall we suppose that a heavenly remedy is meant; whereby those who wished to establish their own righteousness, were so far deserted and blinded, as to stumble on the stumbling stone, till, with confusion of face, they humbled themselves, and sought not their own righteousness which puffeth up the proud, but God’s righteousness, which justifieth the ungodly. For many of those who put Christ to death, were afterward troubled with a sense of their guilt; which led to their believing in Him. (c. 12). These things said Esaias, when he saw His glory, and spake of Him. He saw Him not really, but figuratively, in prophetic vision. Be not deceived by those who say that the Father is invisible, the Son visible, making the Son a creature. For in the form of God, in which He is equal to the Father, the Son also is invisible; though He took upon Him the form of a servant, that He might be seen by men. Before His incarnation too, He made Himself visible at times to human eyes; but visible through the medium of created matter, not visible as He is.”