11 Turn now to the Samaritans, who, receiving the Law only, allow not the Prophets. To them the text just now read from Ezekiel appears of no force, for, as I said, they admit no Prophets; whence then shall we persuade the Samaritans also? Let us go to the writings of the Law. Now God says to Moses, I am the God of Abraham, and of Isaac, and of Jacob; this must mean of those who have being and subsistence. For if Abraham has come to an end, and Isaac and Jacob, then He is the God of those who have no being. When did a king ever say, I am the king of soldiers, whom he had not? When did any display wealth which he possessed not? Therefore Abraham and Isaac and Jacob must subsist, that God may be the God of those who have being; for He said not, “I was their God,” but I am. And that there is a judgment, Abraham shows in saying to the Lord, He who judges all the earth, shall He not execute judgment?
Source: Catechetical Lectures (New Advent)