The Sadducees did not believe in the resurrection (Mark 12:18), so this was not a sincere question about heaven. It was meant to make the resurrection look impossible. They built their case on Moses' own law, which told a man to marry his dead brother's childless widow (Mark 12:19). Barnes says they probably stated "a case as difficult as possible," and "though no such case might have occurred, yet it was supposable." Gill puts their point this way: "She was, according to law, the lawful wife of all seven; what particular and special claim could one have to her above the rest?" Behind the question, Barnes notes, they "supposed that substantially the same state of things takes place in the other world as here."

Jesus first answered with a question: "Do ye not therefore err, because ye know not the scriptures, neither the power of God?" (Mark 12:24). Then He answered directly: "when they shall rise from the dead, they neither marry, nor are given in marriage; but are as the angels which are in heaven" (Mark 12:25). He went on to prove the resurrection from God's words to Moses at the bush and ended, "He is not the God of the dead, but the God of the living: ye therefore do greatly err" (Mark 12:26-27). A scribe who heard them perceived "that he had answered them well" (Mark 12:28).

The Sadducees were drawing on the law in Deuteronomy 25:5-6: if a man died without a child, his brother was to marry the widow, and the firstborn would "succeed in the name of his brother which is dead." Barnes says, "This law was given by Moses in order to keep the families and tribes of the Israelites distinct, and to perpetuate them." The children were reckoned in the dead brother's family line.

The Sadducees denied more than the resurrection of the body. Luke later records that they say "there is no resurrection, neither angel, nor spirit" (Acts 23:8), and Barnes says they denied a future state and the separate existence of the soul after death.

This question shows a common way of resisting God's truth: picture it badly, then reject the picture. Barnes observes that "The way in which the enemies of the truth attempt to make a doctrine of the Bible ridiculous is by adding to it, and then calling it absurd." The Sadducees assumed the life to come must be a copy of this one, with the same marriages and the same legal claims.

Jesus' answer shows that God's power is greater than their imagination. The resurrection life is not a repeat of this life; those raised "are as the angels which are in heaven" (Mark 12:25). And God's word to Moses shows that His relationship with His people does not end at death (Mark 12:26-27).