Isaiah 51:4

"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.

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 as a benevolent accounting; it is the grace from him that went out to illuminate the Gentiles; they were amazed at his judgment, which was both righteous and just—truly the righteousness that is clearly made known in the gospel.

Once it is said in Hebrew: 'Listen,' and secondly according to the Septuagint: 'Hear me, hear me,' so that it may teach us that we should hear with the ears of the body and the understanding of the soul. And a multitude of nations, which is the people of God, is called upon to diligently listen to what is said about it, as Zacharias says: 'Many nations will take refuge in the Lord, and they will become his people' (Zech. II, 11). They are called a people, as some will have it, the remnant of believers of Israel; and for tribe, or race, those who have believed from the multitude of nations, as Moses in Deuteronomy says to the nations in his song: 'Rejoice, O nations, with His people' (Deut. 32:43). For tribe, which we have interpreted as Theodotion, means 'race'; Symmachus translates it as 'nation'; the Seventy, as 'kings'. For we are both tribe and race, and people, and a royal and priestly lineage of the Lord, just as Abraham, who was called a king, and the other saints, of whom it is written: 'Touch not my anointed ones' (Ps. 105:15). What is it that is commanded to be heard? Because the law, he says, will go forth from me, and my judgment into the light of the people, or nations. This law of the Gospel is shown to be spiritual, which will go forth from Zion; not of Moses, which was given of old on Sinai; and my judgment will proceed into the light of the nations, through which it has been established and decreed that all nations will be saved.