Hebrews 8:7-9
But (as I said) he sets down that which especially cheers them, in the words, “Which was established upon better promises.” Whence does appear? In that this the one was cast out, and the other introduced in its place: for it is therefore of force because it is better. For as he says, “If perfection were by” it, “what further need was there, that another priest should rise, after the order of Melchisedec?”; so also here he used the same syllogism, saying “For if that first covenant had been faultless, then should no place have been sought for the second”; that is, if it made men “faultless.” For it is because he is speaking of this that he did not say, “But finding fault with” it, but “But finding fault with them, He says, Behold, the days come, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah: not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt: because they continued not in My covenant, and I regarded them not, says the Lord.”
Yea, verily. And whence does it appear that [the first Covenant] came to an end? He showed it indeed also from the Priest, but now he shows more clearly by express words that it has been cast out.
But how is it “upon better promises”? For how, tell me, can earth and heaven be equal? But do thou consider, how he speaks of promises there [in that other covenant] also, that you may not bring this charge against it. For there also, he says “a better hope, by which we draw near unto God”, showing that a Hope was there also; and in this place “better promises,” hinting that there also He had made promises.
But inasmuch as they were forever making objections, he says, “Behold! The days come, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah.” He is not speaking of any old Covenant: for, that they might not assert this, he determined the time also. Thus he did not say simply, “according to the covenant which I made with their fathers,” lest you should say [it was] the one made with Abraham, or that with Noah: but he declares what [covenant it was], “not according to the covenant which I made with their fathers” in the Exodus. Wherefore he added also, “in the day that I took them by the hand, to lead them out of the land of Egypt; because they continued not in My covenant, and I regarded them not, says the Lord.” You see that the evils begin first from ourselves (“they” themselves first, says he, continued not in [the “covenant”]) and the negligence is from ourselves, but the good things from Him; I mean the [acts] of bounty. He here introduces, as it were, an apology showing the cause why He forsakes them.
Source: Homilies on the Epistle to the Hebrews (New Advent)