Objection 1. It would seem that Christ's persecutors did know who He was. For it is written (Matthew 21:38) that the husbandmen seeing the son said within themselves: "This is the heir; come, let us kill him." On this Jerome remarks: "Our Lord proves most manifestly by these words that the rulers of the Jews crucified the Son of God, not from ignorance, but out of envy: for they understood that it was He to whom the Father says by the Prophet: 'Ask of Me, and I will give Thee the Gentiles for Thy inheritance.'" It seems, therefore, that they knew Him to be Christ or the Son of God.
Objection 2. Further, our Lord says (John 15:24): "But now they have both seen and hated both Me and My Father." Now what is seen is known manifestly. Therefore the Jews, knowing Christ, inflicted the Passion on Him out of hatred.
Objection 3. Further, it is said in a sermon delivered in the Council of Ephesus (P. iii, cap. x): "Just as he who tears up the imperial message is doomed to die, as despising the prince's word; so the Jew, who crucified Him whom he had seen, will pay the penalty for daring to lay his hands on God the Word Himself." Now this would not be so had they not known Him to be the Son of God, because their ignorance would have excused them. Therefore it seems that the Jews in crucifying Christ knew Him to be the Son of God.
On the contrary, It is written (1 Corinthians 2:8): "If they had known it, they would never have crucified the Lord of glory." And (Acts 3:17), Peter, addressing the Jews, says: "I know that you did it through ignorance, as did also your rulers." Likewise the Lord hanging upon the cross said: "Father, forgive them, for they know not what they do" (Luke 23:34).
I answer that, Among the Jews some were elders, and others of lesser degree. Now according to the author of De Qq. Nov. et Vet. Test., qu. lxvi, the elders, who were called "rulers, knew," as did also the devils, "that He was the Christ promised in the Law: for they saw all the signs in Him which the prophets said would come to pass: but they did not know the mystery of His Godhead." Consequently the Apostle says: "If they had known it, they would never have crucified the Lord of glory." It must, however, be understood that their ignorance did not excuse them from crime, because it was, as it were, affected ignorance. For they saw manifest signs of His Godhead; yet they perverted them out of hatred and envy of Christ; neither would they believe His words, whereby He avowed that He was the Son of God. Hence He Himself says of them (John 15:22): "If I had not come, and spoken to them, they would not have sin; but now they have no excuse for their sin." And afterwards He adds (John 15:24): "If I had not done among them the works that no other man hath done, they would not have sin." And so the expression employed by Job (21:14) can be accepted on their behalf: "(Who) said to God: depart from us, we desire not the knowledge of Thy ways."
But those of lesser degree--namely, the common folk--who had not grasped the mysteries of the Scriptures, did not fully comprehend that He was the Christ or the Son of God. For although some of them believed in Him, yet the multitude did not; and if they doubted sometimes whether He was the Christ, on account of the manifold signs and force of His teaching, as is stated John 7:31-41, nevertheless they were deceived afterwards by their rulers, so that they did not believe Him to be the Son of God or the Christ. Hence Peter said to them: "I know that you did it through ignorance, as did also your rulers"--namely, because they were seduced by the rulers.
Reply to Objection 1. Those words are spoken by the husbandmen of the vineyard; and these signify the rulers of the people, who knew Him to be the heir, inasmuch as they knew Him to be the Christ promised in the Law, but the words of Psalm 2:8 seem to militate against this answer: "Ask of Me, and I will give Thee the Gentiles for Thy inheritance"; which are addressed to Him of whom it is said: "Thou art My Son, this day have I begotten Thee." If, then, they knew Him to be the one to whom the words were addressed: "Ask of Me, and I will give Thee the Gentiles for Thy inheritance," it follows that they knew Him to be the Son of God. Chrysostom, too, says upon the same passage that "they knew Him to be the Son of God." Bede likewise, commenting on the words, "For they know not what they do" (Luke 23:34), says: "It is to be observed that He does not pray for them who, understanding Him to be the Son of God, preferred to crucify Him rather than acknowledge Him." But to this it may be replied that they knew Him to be the Son of God, not from His Nature, but from the excellence of His singular grace.
Yet we may hold that they are said to have known also that He was verily the Son of God, in that they had evident signs thereof: yet out of hatred and envy, they refused credence to these signs, by which they might have known that He was the Son of God.
Reply to Objection 2. The words quoted are preceded by the following: "If I had not done among them the works that no other man hath done, they would not have sin"; and then follow the words: "But now they have both seen and hated both Me and My Father." Now all this shows that while they beheld Christ's marvelous works, it was owing to their hatred that they did not know Him to be the Son of God.
Reply to Objection 3. Affected ignorance does not excuse from guilt, but seems, rather, to aggravate it: for it shows that a man is so strongly attached to sin that he wishes to incur ignorance lest he avoid sinning. The Jews therefore sinned, as crucifiers not only of the Man-Christ, but also as of God.
Source: Summa Theologica (New Advent)