Hebrews 8:8

For finding fault with them
Both with the covenant, which had its faults, and with the people who continued not in it, and were therefore disregarded by the Lord, ( Hebrews 8:9 )

he saith, behold, the days come (saith the Lord) when I will make a
new covenant with the house of Israel, and with the house of Judah;
the words are cited from ( Jeremiah 31:31 Jeremiah 31:32 ) in which God promises a "new covenant"; so called, not because newly made; for with respect to its original constitution, it was made from eternity; Christ the Mediator of it, and with whom it was made, was set up from everlasting; and promises and blessings of grace were put into his hands before the world began: nor is it newly revealed, for it was made known to Adam, and in some measure to all the Old Testament saints, though it is more clearly revealed than it was; but it is so called in distinction from the former administration of it, which is waxen old, and vanished away; and with respect to the order of succession, it taking place upon the former being removed; and on account of the time of its more clear revelation and establishment being in the last days; and because of its mode of administration, which is different from the former, in a new way, and by the use of new ordinances; and because it is always new, its vigour and efficacy are perpetual; it will never be antiquated, or give place to another; and it provides for, and promises new things, a new heart, a new spirit to which may be added, that it is a famous, excellent covenant, there is none like it; just as an excellent song is called a new song. The persons with whom this covenant is promised to be made, are the houses of Israel and Judah; which being literally taken, had its fulfilment in the first times of the Gospel, through the ministry of John the Baptist, Christ, and his apostles, by whom this covenant was made known to God's elect among the twelve tribes; but being mystically understood, includes both Jews and Gentiles, the whole Israel of God; Israel not after the flesh, but after the Spirit; such as were Jews inwardly; God's elect of every nation: the word (suntelesw) , rendered, "I will make", signifies, I will consummate, or finish, or end, or fulfil it; which shows the perfection of this covenant, and the imperfection of the former; and that what was typified in the first is fulfilled in this; and that it is now established and ratified by Christ; and is so finished, as to the manifestation and administration of it, that there will be no alteration made in it, nor any addition to it: the time of doing all this is called "the days to come"; the last days, the days of the Messiah, which were future in Jeremiah's time: and a "behold" is prefixed to the whole, as a note of attention, this being an affair of great moment and importance; and as a note of demonstration, or as pointing to something that was desired and expected; and as a note of admiration, it containing things wonderful and marvellous.