Hearken unto me, my people; and give ear unto me, O my nation: for a law shall proceed from me, and I will make my justice to rest for a light of the people.
Read Chapter 51
Cyril of Alexandria
But when the time of his incarnation unexpectedly arrived, then the shadows made way for the truth. And he said, “Listen to me, O my people.” … He is speaking here not only to those who are numbered among the people but also to the kings, because he wanted the rulers, the leaders of the people, to receive his message as well.… “The law will go forth from me, and my judgment will be a light to the nations.” He refers to the divine and evangelical preaching as “law” here; it is just that it is in a different form now, just as the oracles and salvation also are new. For just as the old law was changed to something better, there has also been a transfer from those things that were provisional types to that which is the truth. For Christ said, “Do not think I have come to destroy the law.” … The law in letters was given by Moses, but the preaching of salvation, which is the gospel, came through Christ.… He calls his “judgment” here something that is both sanctioned by the law of God as well...
“Listen to me, my people, and give ear to me, my nation; for a law will go forth from me.” And how could it go forth now, if it were the same law that went forth in the days of Moses? But it is evident that here he mystically signifies the spiritual law, which is the New Testament. “And my justice is a light to the peoples,” that is, my sacrament. He also means that the conscience of the Gentiles, which is now clouded by idolatry, will be enlightened after all their gods are condemned by the divine sentence. - "Commentary on Isaiah 51.4"
In the Septuagint “listen to me” is said twice to teach us that we ought to listen with the ears of our body and with the understanding of our soul.… For “tribe,” as we have translated, Theodotion has “race,” Symmachus “people” and the Septuagint “kings.” For we are a tribe and line and a royal, priestly race of the Lord, such as was Abraham, who was called “king,” and the rest of the saints, concerning whom it is written, “touch not my christs.” - "Commentary on Isaiah 14.7"
The law promulgated on Horeb is now old and belongs to yourselves alone, but this is for all universality. Now, law placed against law has abrogated that which is before it, and a covenant that 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, after which there shall be no law, no commandment or ordinance. Have you not read this, which Isaiah says: “Hearken to me, hearken to me, my people; and your kings, give ear to me: for a law shall go forth from me, and my judgment shall be for a light to the nations.” And Jeremiah, concerning this same new covenant, speaks this way: “Behold, the days come, says the Lord, that 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 that I took them by the hand, to bring them out of the land of Egypt.” - "Dialogue with Trypho 11"