You that say a man should not commit adultery, do you commit adultery? you that abhor idols, do you commit sacrilege?
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Ambrosiaster
AD 400
The Jew adulterates the law by removing the truth of Christ from it and putting lies in his place. In another of his epistles Paul writes: “They are adulterers of God’s Word.” A man is sacrilegious when he denies Christ, whom the law and the prophets call God. Did the Jews ever say, “Thou art God and we did not know it” of God the Father, when the entire law proclaims the authority of God the Father, by whom all things are made? But when the Son of God appeared, what he was was hidden and not revealed until after the resurrection. It was then that it was said of him: “Thou art God and we did not know it.” Commentary on Paul’s Epistles.
Idols The Jews, at the time of our Saviour, were free from idolatry, to which their ancestors had been so prone for so long a time. But to this evil had succeeded another, scarcely less heinous, viz. sacrilege, and a profanation of holy things. The greater part of the high priests bought their office. The priests permitted in the temple itself a kind of traffic, which caused our Saviour to declare to them, that they had made the house of his Father a den of thieves. And to favour their own avarice, they taught that it was lawful to defraud their creditors, and refuse to their parents the necessary succour, in the case of vows to give to the temple. St. Paul does not here reproach them for the profanations of the temple which they committed in the last siege of Jerusalem, for it had not then taken place; but he knew full will the dispositions of their hearts, and the little regard they had for the most sacred things. (Calmet)
It was strictly forbidden for Jews to touch any of the treasures deposited in heathen temples, because they would be defiled. But Paul claims here that the tyranny of greed has persuaded them to disregard the law at this point.