But the main point of the Pharisees was that there is no resurrection of the dead. The passage Christ chooses to quote to prove the resurrection is one that they knew perfectly well, but they had never given it the careful attention it deserved to think through all its implications.
The Sadducees did not believe in an after-life or a resurrection. We do! But we can make the same mistake as the Sadducees. We can greatly err, greatly wander, and this is how. By believing in heaven, the paradise and then ultimately the new heavens and the new earth, the bodily occupation of it, we can believe those things theoretically, without allowing them to mean much to us, without thinking about them very much. Seldom do they play a significant role in our thinking, and that is tragic, because if it were the greatest imaginable mistake for the Sadducees not to believe in heaven at all, we are not far behind them if we believe and yet we do not anticipate heaven and reflect on it.
Some people object to this. They say, ‘The Lord’s answer wasn’t so very good after all for two reasons. God speaking in that way out of the burning bush may have meant, ‘I was the God of your patriarchs, of your fathers.’ But, no, you can’t say that because it’s in the exactly the same passage where God gives to Moses his name: ‘I am.’ There is no question, that when he says ‘I am the God of Abraham,’ that is exactly what he means. He shortly after that pronounced himself to be the ‘I am.’ The ‘I am the God of Abraham’ and so on clearly implies that they are still alive, just as he is alive.
A second objection is this: Yes, but this doesn’t prove the resurrection. It at best only proves that the patriarchs were at that time alive in spirit, as souls in the presence of God. That is true: the patriarchs were not in resurrection bodies at this time, but with God as disembodied souls. It is a sufficient answer to say that God created man as body and spirit, not spirit only. If his soul is alive with God, then God will raise up his body also. But there are also specific promises that are not yet fulfilled that prove the resurrection. The Jews knew that God had made land promises to Abraham, Isaac, and Jacob. Every time God mentions the covenant with Abraham, he says, ‘to thy seed’, to your descendants, will I give it. Now Hebrews tells us that Abraham did not see those promises fulfilled during his earthly life – ‘These all died in faith, not having received the promises, but having seen them afar off’ (Hebrews 11:13) – and yet those promises still stand, and they were made to him personally. Hebrews solves the problem for us: ‘he looked for a city which hath foundations, whose builder and maker is God (Hebrews 11:10)’; and ‘if they had been mindful of that country from whence they came out, they might have had opportunity to have returned. 16 But now they desire a better country, that is, an heavenly: wherefore God is not ashamed to be called their God: for he hath prepared for them a city’ (Hebrews 11:15-16). The land promises will be fulfilled in a newly created and glorified earth. But what is the good of restoring the earth and rejuvenating it and making it a glorious place, if there isn’t going to be a physical occupation of it with resurrected bodies? The land promises to Abraham imply that he will have a physical body to live in that land.