For the modern day Christian, resurrection is a basic principle of belief, but in Jesus' time it was a hot topic, intensely debated between the Pharisees and the Sadducees.
Believe it or not, there is almost no reference to the idea of resurrection in the Old Testament. It seems the Jews just thought people died and that their spirit entered the afterlife existence of Sheol. The Sadducees didn't even believe that. They believed your spirit died with your body and that was the end of the conversation. With this in mind, our ears become wide open as Jesus engages in the topic.