Hebrews 8:8

finding fault with them--the people of the old covenant, who were not made "faultless" by it (Heb 8:7); and whose disregard of God's covenant made Him to "regard them not" (Heb 8:9). The law is not in itself blamed, but the people who had not observed it. he saith-- (Jer 31:31-34; compare Eze 11:19; Eze 36:25-27). At Rama, the headquarters of Nebuzar-adan, whither the captives of Jerusalem had been led, Jeremiah uttered this prophecy of Israel's restoration under another David, whereby Rachel, wailing for her lost children, shall be comforted; literally in part fulfilled at the restoration under Zerubbabel, and more fully to be hereafter at Israel's return to their own land; spiritually fulfilled in the Gospel covenant, whereby God forgives absolutely His people's sins, and writes His law by His Spirit on the hearts of believers, the true Israel. "This prophecy forms the third part of the third trilogy of the three great trilogies into which Jeremiah's prophecies may be divided: Jeremiah 21-25, against the shepherds of the people; Jeremiah 26-29, against the false prophets; Jeremiah 30 and 31, the book of restoration" [DELITZSCH in ALFORD]. Behold, the days come--the frequent formula introducing a Messianic prophecy. make--Greek, "perfect"; "consummate." A suitable expression as to the new covenant, which perfected what the old could not (compare end of Heb 8:9, with end of Heb 8:10). Israel . . . Judah--Therefore, the ten tribes, as well as Judah, share in the new covenant.

— Jamieson-Fausset-Brown Commentary (public domain)