What does Mark 12:20 mean?

The Sadducees are a sect of religious Judaism, like the Pharisees, Zealots, and Essenes. Culturally, the Sadducees tend to be the high priests and the aristocracy of Jerusalem. Theologically, they interpret the Jewish Scriptures—the Old Testament—literally, especially the first five books, the Torah. Since the Torah doesn't mention life after death, and other comments in Jewish Scriptures are vague, the Sadducees do not believe in the resurrection of the dead. This partially explains their tendency toward positions of earthly power and authority.

The Sadducees' disbelief in an afterlife also explains their choice of riddle. The thought of dying without a son would be troubling. If a man ceases to exist after his death, the only legacy he can hope for is through his sons. That is why the concept of a levirate marriage is so important. If a man dies, his younger brother or kinsman redeemer is required by law to marry the widow and provide an heir for the older brother (Deuteronomy 25:5–10). Not only would the older brother have a legacy, the widow would have a son to care for her.

For seven brothers to die with no sons (Mark 12:22) would not only end the line of the sons, it would end the line of their father. This is a situation in which the Sadducees might hope that the resurrection of the dead is true. In this case, however, they just want to discredit Jesus, while trying to paint the idea of resurrection as absurd. If Jesus' popularity continues to grow, and if enough people start believing that He is the Messiah, come to rescue Israel from Roman rule, the Sadducees will quickly lose their Roman allies.