The writer of Hebrews was obviously quoting from Jeremiah 31:31-32. The context of Jeremiah involved the era of Nebuchadnezzar’s capture and eventual destruction of Jerusalem. The LORD had delivered Judah into the hands of the Babylonians, because they had rejected the criteria of the covenant He had made with their ancestors, their “fathers,” some 800 years before. He had given that covenant through Moses and it included both blessings and cursings, all of which were dependent upon their observance of the criteria of the covenant. If from the heart they adhered to the conditions He had expressed, they would be blessed and protected, but if they did not adhere, or kept its conditions with perfunctory external observances, they would lose His protection and be subject to the will of their enemies.
That previous covenant had been conditional, and because of that, God had been unable to bring upon His people the blessings He desired, and had designed, to bring upon them. No fault existed in the covenant or its criteria; the fault was in man. He would not keep the criteria of the covenant, and thereby turned aside the blessing intended for him. God’s desire to bless His people, and indeed all people who would believe Him, was demonstrated in the nature of the “new covenant” He would make. The new covenant would include blessing which was not conditional, as it had been in the old one. The LORD Himself would guarantee the blessing, not upon man’s continuing obedience, but upon His person and faithfulness. Man’s only part in the keeping of the covenant was believing, “causing firmness to,” God. Certainly, the writer of Hebrews identified the “new covenant” with that which had come through the sacrifice of the Son of God. God had paid His own price for the reconciliation of man to Himself, and man could experience that reconciliation, just as the ancient Hebrews had done, by placing their trust in Him and His way.