The point Jesus makes in reply is about their error in saying that there is no resurrection.
A new thought struck me this time through about the nature of the levirate marriage law itself. The Sadducees put this way: "Moses said, If a man die, having no children, his brother shall marry his wife, and RAISE-UP a seed unto his brother." (Mat 22:24) Then after they construct their case of the seven brothers, they ask "Therefore in the RAISING-UP, whose wife shall she be of the seven?" (Mat 22:28)
First, it appears that the point of the law is more than a mechanism to take care of property inheritance rights. Many commentators see only that, and observe simply that this law provides a device to address the strong inheritance concerns of those odd folk in the ancient near east.
But the RAISING-UP language here suggests that by this law, God is doing something larger. The First Husband cannot produce a living seed; he is a man of death and he dies. So God appoints a Second Husband to come and produce a seed of the RAISING UP, children of the resurrection.
The Sadducees are wrong for thinking that the law should lead us to wonder about which husband is the true husband. Even their hypothetical case shows that they have missed the point. All of the husbands in their story are men of death, incapable of producing children of the RAISING-UP. The Sadducees do not know the scriptures and do not know the power of God. The seven impotent brothers are from the number of the Sadducees. So ironically, the Sadducees self-identify as impotent men of death. And that is why they don't recognize that they are talking to the man of life who has come to raise up a seed of life. Here is the brother who will produce sons of the resurrection.
Which I'm thinking is what God put the law there to prepare us to see in the first place.