Matthew 22:32

It should be further considered, that this was said to Moses at a time when those holy Patriarchs had gone to their rest. They therefore of whom He was the God were in being; for they could have had nothing, if they had not been in being; for in the nature of things that, of which somewhat else is, must have itself a being; so they who have a God must themselves be alive, since God is eternal, and it is not possible that that which is dead should have that which is eternal. How then shall it be affirmed that those do not, and shall not hereafter, exist, of whom Eternity itself has said that He is?

God moreover is He who says, I am that I am; (Ex. 3:14.) so that it is impossible that He should be called the God of those who are not. And see that He said not, I am the God of Abraham, Isaac, and Jacob, but The God of Abraham, the God of Isaac, and the God of Jacob. But in another place He said thus, The God of the Hebrews hath sent me unto thee. (Exod. 7:16.) For they who in comparison of other men are most perfect before God, have God entirely in them, wherefore He is not said to be their God in common, but of each in particular. As when we say, That farm is theirs, we show that each of them does not own the whole of it; but when we say, That farm is his, we mean that he is owner of the whole of it. When then it is said, The God of the Hebrews, this shows their imperfection, that each of them has some small portion in God. But it is said, The God of Abraham, the God of Isaac, and the God of Jacob, because each one of these possessed God entirely. And it is to the no small honour of the Patriarehs that they lived to God.

(Vers. 31 seqq.) But concerning the resurrection of the dead, have you not read what was spoken by God, saying to you: I am the God of Abraham, the God of Isaac, and the God of Jacob: God is not the God of the dead, but of the living. And when the crowds heard this, they were amazed at his teaching. To prove the truth of the resurrection, he could have used many other more obvious examples, among which is: The dead will be raised up, and those who are in the graves will rise again (Isaiah 26:19). And in another place: Many of those who sleep in the dust of the earth shall awake: some unto everlasting life, and others unto shame and everlasting contempt (Dan. XII, 2). Therefore, it is asked what the Lord intended by this testimony, which seems ambiguous or not sufficiently related to the truth of the resurrection: I am the God of Abraham, and the God of Isaac, and the God of Jacob; and as if having proclaimed this, he proved what he wanted by immediately adding: God is not the God of the dead, but of the living. Those who also surrounded the turmoil, knowing the mystery, were amazed at his teaching and answers. We have already said above that the Sadducees, confessing neither angel, nor spirit, nor resurrection of bodies, also preached the destruction of souls. These accepted only the five books of Moses, rejecting the prophecies of the prophets. Therefore, it was foolish to present testimonies whose authority they did not follow. Furthermore, in order to prove the eternal nature of souls, he presents the example of Moses: 'I am the God of Abraham, and the God of Isaac, and the God of Jacob' (Exodus 3:6). And immediately he deduces: 'God is not the God of the dead, but of the living,' so that when he has proven that souls continue to exist after death (for it could not be that God would be their God if they did not exist at all), the resurrection of the bodies, which have carried out good or evil deeds along with the souls, would consequently be introduced. In the final part of the first Epistle to the Corinthians, the apostle Paul expands on this topic more fully (1 Cor. XV).