What's the Biggest Discourse in the Book of Matthew?

This is the trickiest of the five great speeches around which the book of matthew is structured. Jesus keeps saying he's going to die, so if he die, how does it play out? There's a lot of questions lingering. And the disciples are going to ask two questions themselves that get us into this big, long speech from jesus. It doesn't seem like that's the precise concern that jesus has in view here.