In these three conversations, most people can understand the point of each teaching. What most readers miss is the divine mystery of revelation itself that ties these teachings together. Your Bible is ink on paper; there’s nothing special about that. It’s not the printing, nor the expensive paper, nor the leather binding that makes it sacred. Nor are the words themselves all that critical, but when you approach the written record of revelation with a heart-led faith in God, the words come to life and speak to your very loudly of things beyond words. Unless revelation comes to life in your soul, the Bible is still just ink on paper. The book itself has no power in itself.
The Sadducees were strict about rejecting everything except the Pentateuch itself. They paid no attention to the prophets and other writings. They did not believe in a spirit realm, per se, but insisted that God is the only spirit being. When humans die, that’s the end of them. So they came to Jesus with a bogus question about eternity.
The question assumes you understand the Mosaic Law regarding inheritance. In the normal course of events, the eldest son marries first. His inheritance is a double portion; any younger brothers get one share each. If he dies childless, the next brother in line takes the first brother’s widow in addition to any other wife he may have married. He is to care for her and impregnate her and raise up children to receive the inheritance of the eldest brother. The only temptation here is that if his brother’s wife has no children, then that double portion is redistributed to the surviving brothers.
In the Sadducees impossible story, seven brothers obey the Law and pass off the first brother’s wife in succession, all seven dying childless. Finally the widow dies. Their question was just plain goofy — to whom is she married in the world to come? Now, the Pharisees would tell you it was the first brother, but Jesus voids the whole question. Only fallen fleshly bodies can reproduce. Resurrected bodies are like angelic bodies, spiritual beings that neither die nor give birth. So there’s no need to be married, either. (Notice that angels cannot have sex or reproduce.)
Then He goes on to slap them upside the head about their false doctrines. Quoting Exodus 3:6, one of the books they accept as Scripture, Jesus notes that Jehovah told Moses He was the God of Abraham, Isaac and Jacob, at that point all dead some 400 years. Yet the Lord would not claim to be the God of someone who didn’t exist. Those three were still alive and in His Presence. The Sadducees knew the words of the Pentateuch, but had rejected the message.
If the crowd of peasants listening were surprised at His authoritative answer to the rulers of the nation, they had more coming. The Pharisees took their turn and we can only guess what they had in mind, but they started off with the question of which was the greatest law. It was a pointless question, but one that was quite commonly debated among them. They used it often in their teaching, as well. Perhaps they hoped to catch Him in something during the debate that should have followed. Jesus didn’t take the bait, but took a different tack entirely, avoiding the standard matrix of judicial precedent.
Quoting from two different passages, Jesus said the first from the Shemah (Deuteronomy 6:4-5) was the greatest, calling for the Covenant Nation to commit themselves completely to Jehovah as their true feudal Master. The second commandment was to love your Covenant brother and sister as yourself (Leviticus 19:18). In other words, treat those under the same covenant as members of your extended family household. Their welfare was yours. Get these two commandments right and you can easily understand everything else in Scripture.
This shut them up, so Jesus took His turn and queried them. His question was technical in the sense of inheritance: Whose authority does the Messiah inherit? The Pharisees gave the obvious answer that it was King David’s royal authority; the Messiah would be King of Israel. Quoting from David’s own psalms, Jesus asked how David could call his own heir “Lord”? There was no Talmudic tradition covering this question, and the Pharisees and Scribes weren’t ready to debate this and give a definitive answer.
It’s very loud and clear: You cannot treat revelation like any other teaching or writing. Reducing Scripture to words and principles insults the God who commissioned the writing. If you do not see beyond the words to the divine moral character of God, then you have no idea what the book says in the first place.