So now that we know that the Sadducees believed that Mosaic law says nothing about resurrection, it is easy to see that they hoped to make a fool of Jesus with their question of the wife who married the seven brother in turn. The Ignatius Study Bible states Jesus' response in a nutshell.
Jesus deals with his objectors on their own terms: first, by denying that marriage exists in the next life and, second, by deliberately citing the Mosaic law against them. The burning bush episode shows that Yaweh identified himself with the patriarchs long after their death (Ex 3:6). If Abraham, Isaac, and Jacob are still with God, then life must endure beyond death and a future resurrection is implied in the Pentateuch.
William Barclay makes an important point about what we learn about Jesus in this session.
It may well be that we find this an arid passage. It deals with burning questions of the time by means of arguments which a rabbi would find completely convincing but which are not convincing to the modern mind. But out of this very aridity there emerges a great truth for anyone who teaches or who wishes to commend Christianity to his fellows. Jesus used arguments that the people he was arguing with could understand. He talked to them in their own language; he met them on their own ground; and that is precisely why the common people heard him gladly.
It occurred to me that this also is why when God speaks to someone individually it is often in a way that only that person can understand. It might not seem significant to anyone else but that is because God's message is tailored specifically for each person.