I've not read straight through the chapter break like I did this time. But this is a clear foreshadowing of his death and resurrection. He talked about his death at the end of chapter 8 and gave a demonstration of his resurrection in chapter 9.
Mark 8:36ff is the most forceful, the clearest definitive statement about following Jesus in the Bible. How easy it is to stop short , to work to save your own life, and give lip service to following Jesus. Oh, God, help me go all the way!
The transfiguration shows many things. Not the least of which is the stupid things people say and do when they are afraid. "Let's build three tents."
I do love the disciples attempts to figure out what they just experience. I think they made progress as they processed what happened on the mountain.