7 This thing has been done even in the first times of the faith. Stephen the Martyr was preaching the Truth, and to minds as though dark, in order to bring them forth into light, was making incantation: when he came to make mention of Christ, whom they would not hear at all, of them the Scripture says what? Of them relates what? “They shut,” he says, “their ears.” But what they did afterwards, the narrative of the passion of Stephen does publish. They were not deaf, but they made themselves deaf....For this thing they did at the point where Christ was named. The indignation of these men was as the indignation of a serpent. Why your ears do ye shut? Wait, hear, and if you shall be able, rage. Because they chose not to do anything but rage, they would not hear. But if they had heard, perchance they would have ceased to rage. The indignation of them was as the indignation of a serpent....
8. “God has broken utterly the teeth of them in their own mouth”. Of whom? Of them to whom indignation is as the similitude of a serpent, and of an asp closing up its ears, so that it hears not the voice of men charming, and of medicine medicated by the wise man. The Lord has done to them what? “Hath broken utterly the teeth of them in their own mouth.” It has been done, this at first has been done, and now is being done. But it would have sufficed, my brethren, that it should have been said, “God has broken utterly the teeth of them.” The Pharisees would not hear the Law, would not hear the precepts of truth from Christ, being like to that serpent and asp. For in their past sins they took delight, and present life they would not lose, that is, joys earthly for joys heavenly....What is, “in their own mouth”? In such sort, that with their own mouth against themselves they should make declaration: He has compelled them with their mouth against themselves to give sentence. They would have slandered Him, because of the tribute: He said not, “It is lawful to pay tribute,” or, “It is not lawful to pay tribute.” And He willed to break utterly their teeth, wherewith they were gaping in order to bite; but in their own mouth He would do it. If He said, Let there be paid to Cæsar tribute, they would have slandered Him, because He had spoken evil to the nation of the Jews, by making it a tributary. For because of sin they were paying tribute, having been humbled, as to them in the Law had been foretold. We have Him, say they, a maligner of our nation, if He shall have bidden us to pay tribute: but if He say, Do not pay, we have Him for saying that we should not be under allegiance to Cæsar. Such a double noose as it were to catch the Lord they laid. But to whom had they come? To Him that knew how to break utterly the teeth of them in their own mouth. “Show to Me the coin,” He says. Why do you tempt Me, you hypocrites? Of paying tribute do ye think? To do justice are you willing? The counsel of justice do ye seek? “If truly justice ye speak, judge right things, you sons of men.” But now because in one way ye speak, in another way judge, hypocrites you are: “Why do you tempt Me, you hypocrites?” Now I will break utterly your teeth in your mouth: “show to Me the coin.” And they showed it to Him. And He says not, it is Cæsar's: but asks Whose it is? In order that their teeth in their own mouth might be utterly broken. For on His inquiring, of whom it had the image and inscription, they said, of Cæsar. Even now the Lord shall break utterly the teeth of them in their own mouth. Now you have made answer, now have been broken utterly your teeth in your mouth. “Render unto Cæsar the things which are of Cæsar, and unto God the things which are of God.” Cæsar seeks his image; render it: God seeks His image; render it. Let not Cæsar lose from you his coin: let not God lose in you His coin. And they found not what they might answer. For they had been sent to slander Him: and they went back, saying, that no one to Him could make answer. Wherefore? Because broken utterly had been the teeth of them in their own mouth. Of that sort is also the following: “In what power doest Thou these things? I also will ask of you one question, answer me.” And He asked them of John, whence was the Baptism of John, from heaven, or of men? So that whatever they might answer might tell against themselves....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)