Heb. 8:8. Behold, the days are coming, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah,
Here he shows more clearly that the Old Testament has been abolished. For he introduces God, speaking through Jeremiah, that "I will make... a new covenant" (Jer. 31:31–34), that is, an entirely new one: not as the Jews understand it, that Ezra renewed the Scripture. For the Scripture did not become new, but remained ancient, even though it was restored by him.
Heb. 8:9. Not such a covenant as I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt, (Cf. Jer. 31:32)
Lest anyone think that the covenant which was made with Abraham is being annulled, he added: "in the day when I took them by the hand." For, he says, I wish to annul the covenant spoken of in the book of Exodus, the covenant given on Mount Sinai to your fathers who cast the calf, whereas it is precisely the covenant with Abraham that received its fulfillment in Christ. For "in your seed," he says, "shall all the nations be blessed" (Gen. 22:18), that is, in Christ.
Heb. 8:9. Because they did not remain in that covenant of Mine, and I disregarded them, says the Lord. (Cf. Jer. 31:32)
Do you see that the beginning of evil is from us? "They," he says, "did not remain," and therefore "I disregarded them." On the contrary, blessings and benefactions receive their beginning from Him. As if justifying Himself, He presents the reason why He abandons them, namely for their inconstancy.
Heb. 8:10. This is the covenant that I will make with the house of Israel after those days, says the Lord: (Cf. Jer. 31:33)
"After those days": which ones? Some say these are the days of the exodus, when the Mosaic law was given. But it seems to me that he is speaking of those days about which he said above: "behold, the days are coming." Thus, after those days have passed, I will establish such a covenant, about which you will hear further.
Heb. 8:10. I will put My laws into their minds, and write them on their hearts; (Jer. 31:33)
Let the Jew show when he received the unwritten law. For even after the return from Babylon, it was given by Ezra in written form. But the Apostles received nothing in written form; rather, they received the law of the Spirit into their hearts. Therefore Christ also said: "The Comforter... will teach you all things and bring all things to your remembrance" (Cf. Jn. 14:26).
Heb. 8:10. And I will be their God, and they shall be My people. (Jer. 31:33)
This was accomplished through the Gospel. For those who formerly served idols, having now recognized the true God, became His people.
Heb. 8:11. And they shall not teach every man his neighbour, and every man his brother, saying, Know the Lord: for all shall know Me, from the least to the greatest. (Cf. Jer. 31:34)
He here calls "learning" an instruction accompanied by labor. For behold, we see that we need a great many words for those of sound mind in order to persuade them to believe in Christ. Since the Jewish law was contained in one corner of the world, few knew it; but the voice of the apostles spread throughout all the earth (Ps. 18:5). And furthermore, since God lived on earth in the flesh, and since He deified our nature through its assumption, He kindled in the souls of all the light of the true knowledge of God, and by grace there was, as it were, implanted in human nature a certain capacity for the true knowledge of God.
Heb. 8:12. Because I will be merciful to their unrighteousnesses, and their sins and their iniquities I will remember no more. (Cf. Jer. 31:34)
Washing us through baptism from the impurity of former sins, He no longer remembers them, as they have already been washed away.
Heb. 8:13. By saying "new," He showed the oldness of the first;
He explains the prophetic expression and says that the very fact that he called this covenant entirely new serves as an indication that the first one ultimately turns out to be old.
Heb. 8:13. But that which is becoming old and aging is near to disappearing.
Having received confidence from the prophet, he finally touches upon the law, showing that our covenant now flourishes. Thus, from the prophetic expression he took the name "old," added on his own the name of obsolescence, and further necessarily drew the conclusion that "destruction" is inevitable for the law, as if saying: it is not by chance that the New Testament abolished the Old, but because of its oldness, its antiquity, that is, by virtue of the fact that it is Old, that is, "weak and unprofitable," as he also says in another place: "the law, weakened by the flesh, was powerless" (Rom. 8:3).