What does Luke 20:30 mean?

From the time of Abraham until Joshua, the Israelites were nomads. While settling in some places for brief periods, the only land they owned was the burial place of Sarah (Genesis 23). The "Promised Land" is just that: land that God promised to give to the Israelites as an inheritance. The ownership of land by tribe, clan, family, and sons was an important part of the culture and the identity of Israel.

A man dying without a son to inherit land was seen as a tragedy. If he had daughters, they could at least marry within the tribe and their husbands could hold the land in his name (Numbers 36). Otherwise, they Israelites practiced "levirate marriage." Under this process, a younger brother would marry his older brother's childless widow with the intent of producing a son—who would be considered the child and heir of the deceased brother. Then, the ownership of the land would continue down the original husband's line (Deuteronomy 25:5–6).

The Sadducees are a religious sect that honors the Mosaic law but does not believe in the resurrection of the dead. They are attempting to use levirate marriage to show that Jesus' teachings—such as resurrection—are false (Luke 20:27–33). They propose this scenario:

A man marries a woman, dies with no heir, and so she marries the next younger brother. That brother dies with no heir, and so forth until the woman has been married to all seven brothers but never had children. Given that scenario, the Sadducees ask, which brother is her husband after the resurrection? Only one—so the other six were false? All of them—so she's married to seven men at once? The real point isn't about levirate marriage, polygamy, or even the resurrection of the dead. It's the Sadducees' attempt to discredit Jesus.

However, the Sadducees have based their argument on a faulty assumption: that "marriage" is a concept that exists in heaven. In fact, it does not.