This is my seventh post for Joe Carter's collaborative project Jesus the Logician (which would better be described as Jesus' Reasoning).
During the week Jesus spent in Jerusalem before his crucifixion, he spent much of his time in the temple disputing with various groups of religious leaders. Much of what we have recorded in the gospels from those discussions is with the Pharisees and scribes. We have only one recorded discussion with the Sadducees, though it appears in all three of the synoptic gospels (Mark 12:18-27, Matthew 22:23-34, and Luke 20:27-40).
The Sadducees were the ruling elite, and they controlled the temple priests. Jesus' challengers in this passage may have been the priests themselves, or they may have been their wealthy benefactors who sided with them against the Pharisees and the Torah experts (often called the scribes). The Sadducees were theologically and religiously conservative. In some ways they were challenging the Pharisaic openness to innovative ideas by insisting on seeing the Torah itself (Genesis through Deuteronomy) as the only infallible guide to theological and ethical belief, just as the Puritans within Anglicanism insisted on not doing anything they couldn't find support for in the Bible as a whole. The Sadducees saw the Pharisees as theological liberals in the same way that the Puritans saw other Anglicans as adding to God's word with liturgical elements and sacramental views that were not biblical.
The Sadducees took this to the point of not recognizing the rest of the Hebrew canon beyond the Torah, so the clearest passages teaching a resurrection (Isaiah 26:19; Daniel 12:2) were not authoritative for them. Even the passages that might easily have a doctrine of resurrection read back into them from an already established view (but that might not establish it on their own, e.g. Psalms 16:9-11; 49:15; 73:23-26; Job 19:25-26; perhaps Ezekiel 37, though that's a vision and can't easily be used to establish much beyond its primary point) are not from the Torah.
The Sadducees try to entrap Jesus in something that will also score them points against their rivals the Pharisees, those theological liberals who also believed in the resurrection. They decided to start with Jesus' claim to a future resurrection and then show that it means he denies the Torah. In Deuteronomy 25:5-6, Moses relates God's regulation of the Levirate custom (which Genesis 38 tells us existed before the Torah). If man died without an heir, and he had a brother living with him, his brother would take over the responsibilities of being a husband to her, both in providing her with children and exercising the responsibilities of fatherhood to those children. The first-born of that marriage, however, would be the heir of the dead brother.
These hardline theological conservatives now try to trap Jesus into denying the Torah teaching on Levirate marriage. The scenario they concoct is remarkably similar to one in the apocryphal book of Tobit, so it's not completely original to them, but this use of it seems to be. Through Levirate marriage, seven men were husbands to the same woman, not one of them having produced the heir before dying without having completed the first Levirate task. The Sadducees then ask Jesus how it is that the resurrection can be possible. Which of the husbands is the woman married to in the resurrection?
The logic of the Sadducees' argument is something like the following:
1. If we believe the Torah teaching on Levirate marriage, then we have to deny the doctrine of the resurrection.
2. The Torah teaching on Levirate marriage is unquestionable.
3. Therefore, the doctrine of resurrection must be wrong.
So it's not just that they don't see biblical support (restricting themselves to the Torah) for the resurrection. They think it contradicts the Torah. Thus they're trying to paint Jesus as denying the Torah through believing in resurrection.
Jesus' response is in two stages. The first would be sufficient to defeat their argument against resurrection, but the second shows that they are the ones who deny the implications of Torah teaching.
Jesus explains that they're giving him a false dilemma. The present him with two options: accept the Torah teaching and deny the resurrection or accept the resurrection but deny the Torah. Jesus' claim is that you can do both. They deny the power of God, he says, in assuming that the resurrection won't involve transformation into something seriously different from this life. Jesus' claim is that there won't be anything like marriage with its exclusivity in the resurrection. That sort of thing will be no more. So it doesn't matter if this woman was married to seven different men in life. In the resurrection she isn't married to any one of them. As far as they're concerned, he hasn't argued that this is correct, but it does show that they haven't presented all the options, which means their trap won't be sprung. He can accept both the resurrection and the Torah.
Jesus' second point makes up for the incompleteness of the first point. To show that they themselves are the ones denying the Torah, he establishes that the Torah itself assumes a resurrection. In talking about the God of Abraham, Isaac, and Jacob, the Torah assumes that Abraham, Isaac, and Jacob are not no more. God is not the God of the dead. God makes a covenant with living people, and that covenant is still in effect. The Sadducees take that covenant to be continued with their descendants but only with those still alive. Abraham, Isaac, and Jacob are no longer in any relation with God, never mind the convenant God had established with them. Why would the Torah speak of God as the God in covenant with them if God were not still in covenant with them, which assumes some sort of immortality beyond what the Sadducees allowed for?
The Greek notion of immortality without a body wouldn't have made sense to the Hebrew mind, according to which the body is a crucial part of the person, so resurrection is really the only option a first century Jew would have considered as an alternative to Sheol (death or the grave) as the final end. So it's not just that Jesus is able to squeeze out of the dilemma with a third option. He shows that the assumption of the Sadducees is false even by their own standards, and they Sadducees therefore are the ones who reject the Torah.
One interesting element of what Jesus is up to here is that he's meeting them on their own terms. He uses a standard rabbinic-style argument based on something from the only five biblical books they consider authoritative. The Greek rhetoriticians would have called this sort of thing paromologia, and the Romans would have called it concessio. It's as if he concedes for the sake of argument that the Torah is the only authoritative book, something they insist on. He can still establish his claim.
You might also think of what Jesus is doing here as something like a reductio ad absurdum, an argument form that starts with the opponent's views and then argues to an absurdity, leading to the opponent's need to deny one of the assumptions. In this case, that assumption would be the Sadducees' denial of the resurrection, since they weren't about to give up the Torah.