What does Matthew 22:29 mean?

Jesus is not fooled by the supposed paradox offered by the Sadducees (Matthew 22:15–28). Instead, He shows that what they see as a contradiction is a misunderstanding. In fact, Jesus harshly criticizes their knowledge of both Scripture and God. His response will correct their mistake (Matthew 2230). It will also turn the tables on them, using the same texts they claim to revere to prove that the resurrection must be real (Matthew 22:31–32).

The Sadducees were inclined to ignore all religious writings except for the Pentateuch: the first five books of the Old Testament, also known as the Law of Moses. Since those books do not directly define the resurrection or afterlife, the Sadducees were able to hold to their conviction about the lack of resurrection. If they had received the writings of the prophets as the revelation of God, these religious leaders would have found many references to the resurrection (Isaiah 26:19; Daniel 12:2; Job 19:25–27).

Jesus also says the Sadducees did not know God's power. This was true in a broad sense: Sadducees were notably more secular than Pharisees and did not believe God was especially involved in daily life. It's to be expected they could not imagine a reality beyond the one they saw on a regular basis. If they had expanded their idea of just how powerful God can be, they might have been able to accept the idea of an unimaginably wonderful eternity for the people of God.