Luke 20:28 is a text that can be used in support of intercession of the saints, because it is saying that all the saints are living in God’s eyes.
The Sadducees believed there was no “resurrection,” which means no physical raising of the body to be reunited with the soul sometime in the future. The word “resurrection” in Greek as well as in Aramaic and Hebrew refer only to that which is corporeal. It means “to stand up again” after having been knocked down in death. Some non-Catholics confuse this word to mean “bring back to life,” as in raising a person to eternal life as a soul in heaven. This is not the meaning of the word because spirits and souls are not corporeal or physical. It can only apply to that which is or once was in such a physical state, not that which does not possess such a state to begin with like a soul or a spirit.
Apparently the Sadducees had a similar misunderstanding of the terminology, for they appear to have had no belief in an afterlife of any kind. They also had an incorrect understanding of God and where we in the temporal order of things fit into God’s scope of the universe and time. To them God was also limited to the passing of time as experienced by human beings. And in this scope of understanding, those who had died were long gone.
Their pride in this understanding was combined with the use of the Pentateuch as a proof text for their beliefs. All their beliefs were based on the first five books of the Bible, the Book of Moses or the Torah. If it was not in the Torah, they did not believe it, or so they claimed.
Jesus saw through their triumphalism by quoting the Torah where God tells Moses at the burning bush: “I am the God of Abraham, the God of Isaac, and the God of Jacob,” not “I was their God.” This was significant, because for the Sadducees, God was supposed to be limited to experiencing things as humans did, to be subject to the passing of time and history.
But here, Jesus pointed out to their surprised silence, that the Torah taught the opposite. To God, Abraham is not dead—even though there has not yet been a resurrection of his body. Was Abraham in heaven? No, for Jesus had not yet died and made this possible. So what was Jesus saying?
That Moses himself testified to the fact that God was superior to the temporal existence, and that there was an afterlife because Abraham, Isaac, and Jacob were there in it, no longer dead from this point of view of God, the real point of view of all things. God is not the God of those who are dead and in the grave and cannot hear our prayers for intercession. God is the God of these people who are living to him because they are truly alive in his presence. In a sense we are all, even though we have yet to enter eternity from our perspective.
Thus the saints are not dead, but alive, experiencing eternity that transcends our temporal world. They are thus very much capable of interceding.
Romans 14:9 is only speaking of things in the temporal and not the eternal state in which God exists. By saying that Jesus is Lord of those who are dead (from our standpoint) and the living (from our standpoint), Paul is commenting that no one is free from submission to Christ’s rule, even if they have died sometime in history’s past. Yes, even those currently dead will have to be subject to Christ one day, just as the living are today. Having died in the past before Christ came to earth does not exempt one from this.
One cannot exercise rule or lordship over those who don’t exist, if death is truly the state of nonexistence. This would mean Christ is not the Lord of those who died, because those who died would no longer exist. He is not the Lord of that which is not.
No, Christ is the Lord of the dead because, as Jesus told the Sadducees, no one is really dead from God’s viewpoint in eternity. We are all very much alive. Christ being God is thus also the God of the living, not the dead, for all are living to him.
And if all are living to him, then the saints can indeed intercede in our behalf.