11 But when he added, “And they should be converted, and I should heal them,” is there a “not” to be understood, that is, they should not be converted, connecting it with the clause before, where it is said, “that they should not see with their eyes and understand with their heart;” for here also it is certainly meant, “and should not understand”? For conversion itself is likewise a gift of His grace, as when it is said to Him, “Turn us, O God of Hosts.” Or may it be that we are to understand this also as actually taking place through the merciful experience of the divine method of healing, [namely this,] that, being of proud and perverse wills, and wishing to establish their own righteousness, they were left alone for the very purpose of being blinded; and thus blinded in order that they might stumble on the stone of stumbling, and have their faces filled with shame; and so, being thus humbled, might seek the name of the Lord, and no longer a righteousness of their own, that inflated their pride, but the righteousness of God, that justifies the ungodly? For this very way turned out to the good of many of them, who were afterwards filled with remorse for wickedness, and believed on Christ; and on whose behalf He Himself had put up the prayer, “Father, forgive them, for they know not what they do.” And it is of that ignorance of theirs also that the apostle says, “I bear them record that they have a zeal of God, but not according to knowledge:” for he then goes on also to add, “For they, being ignorant of God's righteousness, and seeking to establish their own righteousness, have not submitted themselves unto the righteousness of God.”
12. “These things said Isaiah, when he saw His glory, and spoke of Him.” What Isaiah saw, and how it refers to Christ the Lord, are to be read and learned in his book. For he saw Him, not as He is, but in some symbolic way to suit the form that the vision of the prophet had itself to assume. For Moses likewise saw Him, and yet we find him saying to Him whom he saw, “If I have found grace in Your sight, show me now Yourself, that I may clearly see You;” for he saw Him not as He is. But the time when this shall yet be our experience, that same Saint John the Evangelist tells us in his Epistle: “Dearly beloved, [now] are we the sons of God; and it has not yet become manifest what we shall be: because we know that, when He shall appear, we shall be like Him; for we shall see Him as He is.” He might have said “for we shall see Him,” without adding “as He is;” but because he knew that He was seen of some of the fathers and prophets, but not as He is, therefore after saying “we shall see Him,” he added “as He is.” And be not deceived, brethren, by any of those who assert that the Father is invisible, and the Son visible. This assertion is made by those who think that the latter is a creature, and whose understanding runs not in harmony with the words, “I and my Father one.” Accordingly, as respects the form of God wherein He is equal with the Father, the Son also is invisible: but, in order to be seen of men, He assumed the form of a servant, and being made in the likeness of men, became visible to man. He showed Himself, therefore, even before His incarnation, to the eyes of men, as it pleased Him, in the creature-form at His command, but not as He is. Let us be purifying our hearts by faith, that we may be prepared for that ineffable and, so to speak, invisible vision. For “blessed are the pure in heart; for they shall see God.”
13. “Nevertheless among the chief rulers also many believed on Him; but, because of the Pharisees, they did not confess Him, lest they should be put out of the synagogue: for they loved the glory of men more than the glory of God.” See how the evangelist marked and disapproved of some, who yet, he said, believed on Him: who, if ever they did advance though this gateway of faith, would thereby also overcome that love of human glory which had been overcome by the apostle, when he said, “God forbid that I should glory, save in the cross of our Lord Jesus Christ, by whom the world is crucified unto me, and I unto the world.” For to this end also did the Lord Himself, when derided by the madness of human pride and impiety, fix His cross on the foreheads of those who believed on Him, on that which is in a manner the abode of modesty, that faith may learn not to blush at His name, and love the glory of God more than the glory of men.
Source: Tractates on the Gospel of John (New Advent)