Luke 20:37

(de Anna, Serm. 4.) As the saints claim as their own the common Lord of the world, not as derogating from His dominion, but testifying their affection after the manner of lovers, who do not brook to love with many, but desire to express a certain peculiar and especial attachment; so likewise does God call Himself especially the God of these, not thereby narrowing but enlarging His dominion; for it is not so much the multitude of His subjects that manifests His power, as the virtue of His servants. Therefore He does not so delight in the name of the God of heaven and earth, as in that of the God of Abraham, Isaac, and Jacob. Now among men servants are thus denominated by their masters; for we say, 'The steward of such a man,' but on the contrary God is called the God of Abraham.

Or He says this, that after having proved that the souls abide alter death, (which the Sadducees denied,) He might next introduce the resurrection also of the bodies, which together with the souls have done good or evil. But that is a true life which the just live unto God, even though they are dead in the body. Now to prove the truth of the resurrection, He might have brought much more obvious examples from the Prophets, but the Sadducees received only the five books of Moses, rejecting the oracles of the Prophets.

Or to the reason above given the Lord added the testimony of Scripture, Now that the dead are raised, Moses also showed at the bush, (Exod. 3:6.) as the Lord saith, I am the God of Abraham, the God of Isaac, and the God of Jacob. As if he said, If the patriarchs have once returned to nothing so as not to live with God in the hope of a resurrection, He would not have said, I am, but, I was, for we are accustomed to speak of things dead and gone thus, I was the Lord or Master of such a thing; but now that He said, I am, He shows that He is the God and Lord of the living.