The Shame of Christ
It's important that Jesus's transfiguration comes only after he warns Peter not to be ashamed of his impending death. We are reminded that it is easy to promote Christ when Christ's power is obvious. It is easy to proclaim the victory. It is harder to remember that before Christ rose, Jesus was beaten down, alienated, and isolated by the Romans. So perhaps Jesus is reminding Peter that the Gospel will always be found not on the mountaintop, but in the gutter.