From a demonstration (homily) by Aphraates, Bishop (4th century)
Circumcision of the Heart
Law and covenant have been entirely changed. God changed the first pact with Adam, and gave a new one to Noah. He gave another to Abraham, and changed this to give a new one to Moses. When the covenant with Moses was no longer observed, he gave another pact in this last age, a pact never again to be changed.
He established a new law for Adam, that he could not eat of the tree of life. He gave to Noah the sign of the rainbow in the clouds. He then gave Abraham, chosen for his faith, the mark and seal of circumcision for his descendants. Moses was given the Passover lamb, the propitiation for the people.
All these covenants were different from each other. Moreover, the circumcision that is approved by the giver of those covenants is of the kind spoken of by Jeremiah: Circumcise your hearts. If God’s pact with Abraham was firm, so also is this covenant firm and trustworthy, nor can any other law be laid down, whether it originates outside the law or among those subject to the law.
God gave Moses a law together with his prescriptions and precepts, and when it was no longer kept, he made the law and its precepts of no avail. He promised a new covenant, different from the first, though the giver of both is one and the same. This is the covenant that he promised: All shall know me from the least to the greatest. In this covenant there is no longer any circumcision of the flesh, any seal upon the people.
We know, dearly beloved, that God established different laws in different generations which were in force as long as it pleased him. Afterward they were made obsolete. In the words of the apostle: In former times the kingdom of God existed in each generation under different signs.
Moreover, our God is truthful and his commandments are most trustworthy. Every covenant was proved firm and trustworthy in its own time, and those who have been circumcised in heart are brought to life and receive a second circumcision beside the true Jordan, the waters of baptism that bring forgiveness of sins.
Jesus, son of Nun, renewed the people’s circumcision with a knife of stone when he had crossed the Jordan with the Israelites. Jesus, our Saviour, renews the circumcision of the heart for the nations who have believed in him and are washed by baptism: circumcision bythe sword of his word, sharper than any two-edged sword.
Jesus, son of Nun, led the people across the Jordan into the promised land. Jesus, our Saviour, has promised the land of the living to all who have crossed the true Jordan, and have believed and are circumcised in heart.
Blessed, then, are those who are circumcised in heart, and have been reborn in water through the second circumcision. They will receive their inheritance with Abraham, the faithful leader and father of all nations, for his faith was credited to him for righteousness.
"Lord Jesus, our Savior, let us now come to you: Our hearts are cold; Lord, warm them with your selfless love. Our hearts are sinful; cleanse them with your precious blood. Our hearts are weak; strengthen them with your joyous Spirit. Our hearts are empty; fill them with your divine presence. Lord Jesus, our hearts are yours; possess them always and only for yourself." (Prayer of Augustine, 354-430)
"God expects that the one who loves Him will want to go beyond his human capabilities. He will agree to be totally stripped of all that he is and of all that he possesses, in order that he may become a sign, so that God can become a living presence in the world through him." (The Gift of Faith, pg. 129)