What does Luke 20:29 mean?

The Sadducees are trying to discredit Jesus and His teachings, using what they see as an absurd implication of belief in resurrection (Luke 20:27). They base this on the idea of levirate marriage. In their scenario, a woman marries the oldest of several brothers, but he dies with no children. As the Mosaic law dictates (Deuteronomy 25:5–6), she marries the next youngest brother, who is obligated to provide her with a son who will inherit his brother's place in the family. But he dies as well. This repeats over and over, until she has married seven brothers before herself passing away.

The Sadducees pose the question of which brother will be the woman's husband after the resurrection. It's not really a "question," but a claim that the situation is ridiculous. The thought of a woman with seven husbands is unfathomable, as is the thought of a man sharing his wife with his six brothers. In their minds, this proves that Jesus' teaching about the resurrection is silly, so they shouldn't follow Him.

Like other critics before them (Luke 20:1–26), these men are trying to pull the common people away from Jesus. Too many are starting to follow Him. The Sadducees are so wrapped up in their sectarian and cultural beliefs that they can't see a simple truth that destroys their argument: that there is no marriage in heaven.