Justin Martyr on the New Covenant in 160CE

I have read that there shall be a final law, and a covenant, the chiefest of all, which it is now incumbent on all men to observe, as many as are seeking after the inheritance of God. For the law promulgated on Horeb is now old, and belongs to yourselves alone; but this is for all universally. Now, law placed against law has abrogated that which is before it, and a covenant which comes after in like manner has put an end to the previous one; and an eternal and final law—namely, Christ —has been given to us, and the covenant is trustworthy…

God proclaimed a new covenant which was to be instituted, and this for a light of the nations, we see and are persuaded that men approach God, leaving their idols and other unrighteousness, through the name of Him who was crucified, Jesus Christ, and abide by their confession even unto death, and maintain piety. Moreover, by the works and by the attendant miracles, it is possible for all to understand that He is the new law, and the new covenant, and the expectation of those who out of every people wait for the good things of God. For the true spiritual Israel, and descendants of Judah, Jacob, Isaac, and Abraham (who in uncircumcision was approved of and blessed by God on account of his faith, and called the father of many nations), are we who have been led to God through this crucified Christ, as shall be demonstrated while we proceed.

I also adduced another passage in which Isaiah exclaims: “ ‘Hear My words, and your soul shall live; and I will make an everlasting covenant with you, even the sure mercies of David. Behold, I have given Him for a witness to the people: nations which do not know You shall call on You; peoples who do not know You shall escape to You, because of Your God, the Holy One of Israel; for He has glorified You.’ This same law you have despised, and His new holy covenant you have slighted; and now you neither receive it, nor repent of your evil deeds. ‘For your ears are closed, your eyes are blinded, and the heart is hardened,’ Jeremiah has cried; yet not even then do you listen. The Lawgiver is present, yet you do not see Him; to the poor the Gospel is preached, the blind see, yet you do not understand.