Jesus doesn't dwell a lot on the afterlife, he mostly talks about what life looks like while we're here. This session with the Sadducees is a moment where he decided to talk a bit about life and death. If God weren't the God of the resurrection, how could he remain the God of Abraham, Isaac, and Jacob? As Jesus pointed out, God wasn't the god of the dead. For him to be the God of these three (and their descendants), there must be some scenario where they aren't simply gone. One day we will all enjoy a new Heaven and new earth, and resurrection will remake us all. Even Abraham, Isaac, and Jacob.