Theophylact of Ohrid — as excerpted in the Catena Aurea on Luke 20:27-40

“Or to the reason above given the Lord added the testimony of Scripture, Now that the dead are raised, Moses also shewed 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 shews that He is the God and Lord of the living. This is what follows, But he is not a God of the dead, but of the living: for all live unto him. For though they have departed from life, yet live they with Him in the hope of a resurrection.”