“In the passage about the bush... for all live to him”
Even Moses demonstrates that the dead are raised, in the passage about the burning bush. For he calls the Lord 'the God of Abraham, the God of Isaac, and the God of Jacob.' He is not the God of the dead, but of the living, for to Him all are alive. (Luke 20:27–38 BSB)
What it sounds like today
The seven-brothers puzzle looks bizarre, and Jesus' answer seems to dodge it.
The cultural key
The Sadducees' riddle is built on levirate marriage (Deuteronomy 25:5–6): a man must marry his brother's childless widow to raise an heir. The Sadducees, the temple aristocracy, accepted only the books of Moses as fully authoritative and denied resurrection, so their puzzle is a reductio: whose wife in the resurrection? Jesus answers from their own turf, the Torah itself: at the bush (Exodus 3:6), God says 'I am', present tense, 'the God of Abraham,' centuries after Abraham died. Luke keeps the citation-by-landmark ('in the passage about the bush') and adds the closing theology Matthew lacks: 'for all live to him,' the patriarchs alive to God now, not merely due for revival later.
Recovered meaning
God does not introduce himself by dead men's names. If he still calls himself Abraham's God, Abraham is not gone; covenant relationship outlives the grave. A resurrection proof drawn from the only scriptures his opponents fully conceded.