The Sadduccess ask Jesus a hypothetical question about heaven (which they don't even believe in). Despite their arrogant hypocrisy, Jesus is willing to engage with them - and do so on their own terms. They only believed the first 5 books of the Bible were inspired. Jesus shows them their error by using only the first 5 books of the Bible. Most of us have a tough time dialoguing with folks who disagree with our beliefs. Our default as human beings is to believe that WE have somehow arrived at the "Truth" through our intellectual or moral prowess. This applies to liberals or conservatives, secular or religious folk. Therefore, if anyone disagrees with MY achievement of spiritual, political, or intellectual enlightenment we take it personally and get defensive.
The ego-liberating message of the Gospel is that God substituted us with Christ. We believe our goodness, virtue, value (save-ability) is a gift based on the merits of Christ alone, not our moral devotion. Thus we can't look down upon those less devoted than we are as if we had any part in our acceptability. To take it even further, we can't look down on people who believe differently, as if we had any part in believing ourselves. Even our very faith is a gift of God.