42 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:
[AD 407] John Chrysostom on John 12:37-43
(Hom. lxviii. 1) But why did He hide Himself, when they neither took up stones to cast at Him, nor blasphemed? Because He saw into their hearts, and knew the fury they were in; and therefore did not wait till they broke out into act, but retired to give their envy time to subside.

(Hom. lxviii. 1) And thus the Evangelist tacitly explains it, when he adds, But though He had done so many miracles before them, yet they believed not on Him.

(Hom. lxviii. 2) But why then did Christ come? Did He not know that they would not believe in Him? Yes: the Prophets had prohibited this very unbelief, and He came that it might be made manifest, to their confusion and condemnation; That the saying of Esaias the prophet might be fulfilled, which He spake, Lord, who hath believed our report? and to whom hath the arm of the Lord been revealed?

(Hom. lxviii. 2) That the saying of Esaias might be fulfilled: that here is expressive not of the cause, but of the event. They did not disbelieve because Esaias said they would; but because they would disbelieve, Esaias said they would.

(Hom. lxviii. 2) This is a common form of speech among ourselves. I cannot love such a man, meaning by this necessity only a vehement will. The Evangelist says could not, to show that it was impossible that the Prophet should lie, not that it was impossible that they should believe.

(Hom. lxviii) For He does not leave us, except we wish Him, as He saith in Hosea, Seeing thou hast forgotten the law of thy God, I will also forget thy children. (Hos. 4:6) Whereby it is plain that we begin to forsake first, and are the cause of our own perdition. For as it is not the fault of the sun, that it hurts weak eyes, so neither is God to blame for punishing those who do not attend to His words.

(Hom. lxviii. 2) His glory means the vision of Him sitting on His lofty throne: I saw the Lord sitting upon a throne. Also I heard the voice of the Lord, saying, Whom shall I send, and who will go for us? (Is. 6:1)

[AD 430] Augustine of Hippo on John 12:37-43
(Tr. liii. 2) It is evident here that the arm of the Lord is the Son of God Himself. Not that the Father has a human fleshly form; He is called the arm of the Lord, because all things were made by Him. If a man had power of such a kind, as that without any motion of his body, what he said was forthwith done, the word of that man would be his arm. Here is no ground to justify, however, the error of those who say that the Godhead is one Person only, because the Son is the arm of the Father, and a man and his arm are not two persons, but one. These men do not understand, that the commonest things require to be explained often by applying language to them taken from other things in which there happens to be a likeness, [cand that, when we are upon things incomprehensible, and which cannot be described as they actually are, this is much more necessary. Thus one man calls another man, whom he makes great use of, his arm; and talks of having lost his arm, of having his arm taken away from him.] But some mutter, and ask, What fault was it of the Jews, if it was necessary that the sayings of Esaias should be fulfilled? We answer, that God, foreseeing the future, predicted by the Prophet the unbelief of the Jews, but did not cause it. God does not compel men to sin, because He knows they will sin. He foreknows their sins, not His own. The Jews committed the sin, which He who knows all things foretold they would commit.

(Tr. liii. 5) But what follows involved a deeper question: Therefore they could not believe, because that Esaias said again, He hath blinded their eyes, and hardened their hearts, that they should not see with their eyes, nor understand with their heart, and be converted, and I should heal them. That they should not believe; but if so, what sin is there in a man doing what he cannot help doing? And what is a graver point still, the cause is assigned to God; since He it is who blinded their eyes, and hardened their heart. This is not said to be the devil's doing, but God's. Yet if any ask why they could not believe, I answer, Because they would not. For as it is to the praise of the Divine will that God cannot deny Himself, so is it the fault of the human will that they could not believe.

(Tr. liii. 5) But the Prophet, you say, mentions another cause, not their will; viz. that God had blinded their eyes, and hardened their heart. But I answer, that they well deserved this. For God hardens and blinds a man, by forsaking and not supporting him; and this He may by a secret sentence, by an unjust one He cannot.

(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.

(Tr. liii. 13) As their faith grew, their love of human praise grew still more, and outstripped it.

[AD 804] Alcuin of York on John 12:37-43
Who, i. e. so very few believed.

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 praise of men more than the praise of God. The praise of God is publicly to confess Christ: the praise of men is to glory in earthly things.

[AD 1107] Theophylact of Ohrid on John 12:37-43
He means the miracles related above. It was no small wickedness to disbelieve against such miracles as those.

[AD 407] John Chrysostom on John 12:42
1. It is necessary for us to avoid alike all the passions which corrupt the soul, but most especially those, which from themselves generate numerous sins. I mean such as the love of money. It is in truth of itself a dreadful malady, but it becomes much more grievous, because it is the root and mother of all mischiefs. Such also is vainglory. See, for instance, how these men were broken off from the faith through their love of honor. Many, it says, of the chief rulers also believed on Him, but because of the Jews they did not confess Him, lest they should be put out of the synagogue. As He said also to them before, How can you believe which receive honor one of another, and seek not the honor that comes from God only? John 5:44 So then they were not rulers, but slaves in the utmost slavery. However, this fear was afterwards done away, for nowhere during the time of the Apostles do we find them possessed by this feeling, since in their time both rulers and priests believed. The grace of the Spirit having come, made them all firmer than adamant. Since therefore this was what hindered them from believing at this time, hear what He says.
[AD 428] Theodore of Mopsuestia on John 12:42
Then the Evangelist said that many among the authorities who believed in him hid their opinion about him because of the Pharisees, because they feared they might lose their privileges and because they valued the glory of people more than the glory of God. What did our Lord say? While some believed, others did not even accept the accomplished miracles, others only came to know the truth through the miracles but hid their opinion because of their fear of the Pharisees as they pursued human glory.

[AD 444] Cyril of Alexandria on John 12:42
Now, however, when constrained by the signs to believe and no longer daring to gainsay the Lord, they fail of eternal life through the persistence of their own abominable perversity in esteeming their position in the eyes of men higher than their relationship to God, and in being slaves of a temporal glory, deeming it an intolerable loss to fail of honour at the hands of the Pharisees. Forasmuch therefore as this was what hindered them from believing, hear what the Christ says:----