What does Mark 12:27 mean?

The Sadducees have used a law about marriage to try to disprove the existence of the afterlife (Mark 12:18–23). In response, Jesus quotes the words God used to identify Himself to prove the resurrection is real. This confrontation illustrates the difference between eisegesis and exegesis. These are also described as "reading into" and "reading from" a text.

Eisegesis interprets Scripture through a preconceived worldview. It uses Scripture out of context to prove a belief. The belief comes first, and the written text is interpreted so that it agrees with the preconceived notion. In this case, the Sadducees believe that we cease to exist after we die. To prove that belief, they scour the Old Testament for a passage that confirms their bias.

What they find is the passage on levirate marriages. If a woman's husband dies before she has children, she is to marry the man's brother. In this way, she doesn't have to leave the security of her in-law's home, she gains a son to care for her, and her first husband gains an heir. The Sadducees' hypothetical situation is that a woman's husband dies and she winds up marrying six of his brothers with no children. Since the idea of a woman being married to seven men in the afterlife seems ridiculous, the Sadducees infer there must not be an afterlife.

Jesus uses the biblical interpretation method of exegesis. Exegesis understands the passage in context, as it is presented and intended, and derives spiritual truths from the passage itself. Jesus uses Exodus 3:6 to show that God declared that He is still the God of those who had physically died. If He is still their God, they must still exist, so there must be an afterlife. An exegetical interpretation of the law doesn't deduce that levirate marriages prove the afterlife doesn't exist, it deduces that in the afterlife there is no marriage (Mark 12:24–25).

The same mistake made by the Sadducees is often committed by modern critics of the Bible. They deduce an absurd conclusion, and fail to realize that the absurdity only disproves their assumptions, not Scripture itself.