Our evangelical gospel is a death gospel. "Are we ready for what happens after we die?" Afterlife is the goal of every choice we make now, so this gospel goes. Now is only the precursor and grim necessity for what will come after death.
Like the Saducees in this story, we have been taught to believe or in this case, not believe in the resurrection of the dead. And this struggle is even before we add the account of Jesus' own resurrection.
So given the opportunity to establish a strong foundation for both his followers and critics to have a focus on post-death issues, Jesus instead re calibrates magnetic north for them and us.
Life in God is present for us as it was for Abraham in his day, Isaac in his day, and Jacob in his day. Not only is a death gospel wrong, according to this Scripture it's "quite wrong"! God is the god of those who live, not those who live waiting to die so something else might happen.