What does Luke 20:35 mean?

Jesus disarms an attack from the Sadducees with this statement. They are trying to show that a major post of Jesus' theology, the resurrection of the dead, is inconsistent with the Mosaic law. Their proof scenario is a woman who follows the practice of levirate marriage, marrying seven brothers in turn with no child. If they all rise from the dead, whose wife will she be (Luke 20:27–33)? As those who rejected resurrection, the Sadducees considered this an absurdity and evidence that there could be no future life for the dead.

Jesus explains that the woman won't be anyone's wife after resurrection. Neither will the men be anyone's husband. There is no marriage in the resurrection. The meaning and purpose of marriage are applied in earthly life, not in eternity. The Sadducees' assumptions about life after death are inaccurate, and correcting that error nullifies their challenge (Luke 20:34).

And yet, Jesus will not stop there. The Sadducees might not accept His claims about marriage. But they are bound to accept what's written in the Law of Moses: the first five books of Scripture. Jesus will use the Mosaic law to prove the Sadducees wrong about resurrection. God told Moses that He "is" the God of Abraham, Isaac, and Jacob. This used the present tense, despite being stated hundreds of years after those patriarchs had died. God is the God of the living, not the dead. So, the patriarchs must be alive (Luke 20:37–38).

In Matthew, Jesus prefaces His answer by saying, "You are wrong, because you know neither the Scriptures nor the power of God" (Matthew 22:29). The Sadducees' failure is greater than they can admit. Jesus has used the law they claim to follow to prove they will be resurrected. And if they are resurrected, they will be judged. The Sadducees don't believe God will judge and reward people after they die. Jesus has proved them wrong. And, still, they will conspire to kill Him.