"The covenant of the Lord" of Saint Irenaeus, bishop

In Deuteronomy Moses says to the people: «The Lord our God has established a covenant with us on the Horeb. The Lord did not establish this covenant with our fathers, but with us who are here all alive today "(Dt 5, 2-3).
Why then did he not make the covenant with their fathers? Precisely because "the law is not made for the just" (1 Tim 1: 9). Now their fathers were righteous, they who had written the virtue of the Decalogue in their hearts and souls, because they loved God who created them and refrained from any injustice against their neighbor; therefore it was not necessary to admonish them with corrective laws, since they carried within themselves the justice of the law.
But when this justice and love for God fell into oblivion or rather became extinct in Egypt, God for his great mercy towards men manifested himself by making his voice heard. With his power he led the people out of Egypt to make man become a disciple and follower of God. He chastised the disobedient so that they did not despise the one who created them.
He then fed the people with manna to receive spiritual food as Moses said in Deuteronomy: «He fed you manna, which you did not know and that even your fathers had never known, to make you understand that man it lives not only on bread, but on what comes out of the mouth of the Lord "(Dt 8, 3).
He commanded the love of God and suggested the justice due to the neighbor so that man was not unjust and unworthy of God. Thus he prepared, through the decalogue, the man for his friendship and concord with his neighbor. All this benefited man himself, without God needing anything from man. These things then made man rich because they gave him what he lacked, that is, the friendship of God, but they did not bring anything to God, because the Lord did not need man's love.
On the other hand, man was devoid of the glory of God, who could not acquire in any way except by means of that respect which is due to him. And for this Moses says to the people: "Choose life, therefore, so that you and your descendants live, loving the Lord your God, obeying his voice and keeping you united to him, since he is your life and longevity" ( Deut 30, 19-20).
In order to prepare man for this life, the Lord himself uttered the words of the decalogue for all without distinction. Therefore they remained with us, after having received development and enrichment, certainly not alterations and cuts, when he came into the flesh.
As for the precepts limited to the ancient state of servitude, they were separately prescribed by the Lord to the people by means of Moses in a way suitable for their education and training. Moses himself says so: The Lord then ordered me to teach you laws and rules (cf. Dt 4, 5).
For this reason what was given to them for that time of slavery and in figure, was abolished with the new covenant of freedom. Those precepts, however, which are inherent in nature and which are free men are common to all and were developed with the broad and generous gift of the knowledge of God the Father, with the prerogative of adoption as children, with the granting of perfect love and following faithful to his Word.