Matthew 22:31

And again by Moses doth He stop their mouths, since they too had brought forward Moses; and He saith, "But as touching the resurrection of the dead, have ye not read, I am the God of Abraham, and the God of Isaac, and the God of Jacob? He is not the God of the dead, but of the living." Not of them that are not His meaning is, and that are utterly blotted out, and are to rise no more. For He said not, I was, but, I am; of them that are, and them that live. For like as Adam, although he lived on the day that he ate of the tree, died in the sentence: even so also these, although they had died, lived in the promise of the resurrection. How then doth He say elsewhere, "That He might be Lord both of the dead and of the living?" But this is not contrary to that. For here He speaks of the dead, who are also themselves to live. And moreover too, "I am the God of Abraham," is another thing from, "That He might be Lord both of the dead and of the living." He knew of another death too, concerning which He saith, "Let the dead bury their dead."

In proof of the resurrection there were many plainer passages which He might have cited; among others that of Isaiah, The dead shall be raised; they that are in the tombs shall rise again: (Is. 26:19. juxta LXX.) and in another place, Many of them that sleep in the dust of the earth shall awake. (Dan. 12:2.) It is enquired therefore why the Lord should have chosen this testimony which seems ambiguous, and not sufficiently belonging to the truth of the resurrection; and as if by this He had proved the point adds, He is not the God of the dead, but of the living. We have said above that the Sadducees confessed neither Angel, nor spirit, nor resurrection of the body, and taught also the death of the soul. But they also received only the five books of Moses, rejecting the Prophets. It would have been foolish therefore to have brought forward testimonies whose authority they did not admit. To prove the immortality of souls therefore, He brings forward an instance out of Moses, I am the God of Abraham, &c. and then straight subjoins, He is not the God of the dead, but of the living; so that having established that souls abide after death, (forasmuch as God could not be the God of those who had no existence any where,) there might fitly come in the resurrection of bodies which had together with their souls done good or evil.

(in Joan. Tr. xi. 8.) God is therefore called in particular The God of Abraham, the God of Isaac, and the God of Jacob, because in these three are expressed all the modes of begetting the sons of God. For God begets most times of a good preacher a good son, and of a bad preacher a bad son. This is signified in Abraham, who of a free woman had a believing son, and of a bondslave an unbelieving son. Sometimes indeed of a good preacher He begets both good and bad sons, which is signified in Isaac, who of the same free woman begot one good and the other bad. And sometimes He begets good sons both of good and bad preachers; which is signified in Jacob, who begot good sons both of free women and of bondmaids.

These things which are spoken concerning the conditions of the resurrection He spoke in answer to their enquiry, but of the resurrection itself He replies aptly against their unbelief.