“The first thing I talked about with Rian was the mirror cave … What are Rey’s conflicts? This image reflects a little bit of the Kylo/Rey Force connections, as well as the duality of light and dark, good and evil. Some of these were being pulled from what I knew of The Force Awakens, but also little glints of information from Rian and mirroring the cave in Empire.” — James Clyne, VFX art director, The Art of Star Wars: The Last Jedi
“The idea is this island has incredible light and the first Jedi temple up top, and then it has an incredible darkness that’s balanced down underneath in the cave … In this search for identity, which is her whole thing, she finds all these various versions of ‘Who am I’ going off into infinity, all the possibilities of her. She comes to the end, looking for identity from somebody, looking for an answer, and it’s just her.” — Rian Johnson (x)
“The idea that if there’s a Jedi Temple up top, the light, it has to be balanced by a place of great darkness. We’re drawing a very obvious connection to Luke’s training and to Dagobah here, obviously. And so the idea was if the up top is the light, down underneath is the darkness. And she descends down into there and has to see, just like Luke did in the cave, her greatest fear. And her greatest fear is [that], in the search for identity, she has nobody but herself to rely on.” — Rian Johnson (x)
Some (long, rambling) thoughts on the mirror cave sequence below the cut.