Is the God of the Dead the same deity as the God of the Living in Mark 12:19-27?
Mark 12:26 (KJV) 26 And as touching the dead, that they rise: have ye not read in the book of Moses, how in the bush God spake unto him, saying, I [am] the God of Abraham, and the God of Isaac, and the God of Jacob?
Mark 12:27 (KJV) 27 He is not the God of the dead, but the God of the living: ye therefore do greatly err.
In Mark 11:27-12:44, Jesus is in the temple, where the Pharisees, scribes and Sadducees try to trick him into error, with one question after another. The question of the Sadducees is divided into three parts: 12:19 is a quotation from Deuteronomy; 12:20-22 is the narrative of a case; and 12:23 is the trick question by which they hope to catch him. The Sadducees did not believe in resurrection of the dead, and here they think that there is an insuperable contradiction between the Deuteronomic command for a man to marry his dead brother's wife if she has no children, and the resurrection.
Jesus treats this as two questions and gives two answers. In 12:25, he says that when they rise from the dead they are like angels, neither married nor given in marriage. The answer in 12:26-27 turns the question back on the Sadducees.
The Sadducees think of Abraham, Isaac and Jacob as simply dead, which means that when God had said, "I am the God of Abraham, Isaac and Jacob," he was the God of the dead. But Jesus' notion of resurrection means that Abraham, Isaac and Jacob are not really dead, but alive, and so God is the God of the living.
There is no sense in this passage of one God of the dead and one God of the living. It is a carefully constructed philosophical discussion that there is no God of the dead, only of the living. In Mark's Gospel, Jesus has proven his point by showing that the resurrection is real, as confirmed by verse 12:28 ("perceived that he had answered them well"). So, Jesus is able to tell the Sadducees their understanding is greatly in error.
Many, including myself, have been thrown by the phrase "all live to him". His point was that just because they were all Jews and all had the Torah, the covenants, the promises, etc., "not all Israel is Israel" nor all "sons of the resurrection". The "all" in "all live to him" refer ONLY to the patriarchs (in that context) and "those who attain to the resurrection" in the broader context:
[Luk 20:34-38 ASV] (34) And Jesus said unto them, The sons of this world marry, and are given in marriage: (35) but they that are accounted worthy to attain to that world, and the resurrection from the dead, neither marry, nor are given in marriage: (36) for neither can they die any more: for they are equal unto the angels; and are sons of God, being sons of the resurrection. (37) But that the dead are raised, even Moses showed, in the place concerning the Bush, when he calleth the Lord the God of Abraham, and the God of Isaac, and the God of Jacob. (38) Now he is not the God of the dead, but of the living: for all live unto him.
IE: all of the sons of the resurrection, including Abraham, Isaac and Jacob are God's people and sons of the resurrection - and live to him.
Contrast that with "the dead":
[Luk 9:60 CSB] (60) But he told him, "Let the dead bury their own dead, but you go and spread the news of the kingdom of God."
Mark 12
God is the sacrifice. Both are nouns.
You’re actually reading an English translation that had two choices. Either the abbreviation ΘC was God or sacrifice.
The earliest Greek translation abbreviated the word sacrifice as ΘC. The earliest Greek texts abbreviated the noun sacrifice.
Θεὸς (God) and θυσίας (sacrifice), both could be abbreviated as ΘC, because at the time the Greek alphabet was all capital letters. It was in fact greatly because of Christian theology that the lowercase Greek alphabet had to be invented to distinguish between gnostic meanings of abbreviated capital words.
Mark 12:27
He is not the Sacrifice of the dead, but the Sacrifice of the living: ye therefore do greatly err.
As the Greeks equated sacrificing and god, the verse explains how Jesus being the sacrifice was equated as being God. The dead cannot sacrifice, only the living can sacrifice. The action of animal sacrifices began with Abraham and continued. Jesus does not support the practices of animal sacrifices and he states a prophecy that the Sadducees will sacrifice him which will make him God.
