If you haven't seen Star Wars: The Last Jedi, you may not wish to read further - cause SPOILER ALERT.
On Ahch-To Rey finds Luke Skywalker as well as the very birthplace of the Jedi Order. They have a cool ancient tree with ancient Jedi holy books and all kinds of cool stuff. A place of great Light. In her first Force lesson from Luke, Rey is almost sucked into a place of great Darkness, underneath the island. She feels it had something to show her. Luke was appalled that Rey had no resistance to the Dark side of the Force. Later Rey seeks this place out on her own, goes for an inadvertent dive, and ends up in an underground cavern. In the underworld. A very interesting scene plays out.
Rey finds herself in a seemingly infinite line of selves. Each action she makes is made by her other selves, each with slight delay, as dominoes falling. I could not help but think here, and throughout the movie of Nietzsche's Eternal Recurrence.
Rather than feel trapped, Rey's consciousness seeks out the end of the causal self or the ego self. In Hermetic Qabalah, we could think of this as coming to the Veil of Paroketh. In the movie Rey actually walks up to a veil. This veil, in Hermetic Qabalah, is on the path of Samekh between the two Sephiroth called Yesod and Tiphareth. Paroketh sits between the Sun and Moon. Between consciousness and subconscious. It is the veil that, going down the Tree of Life, is the mirror of the Abyss. Going up the Tree, it is the veil that separates us from out Holy Guardian Angel, our True Self, whatever you want to call it.
The point is, there is a dweller on this threshold. The Jungian Shadow. The Hermetic Dominis Liminis. If we think back to the planet Dagobah, where Luke received his training from Yoda, Luke too was sent down into a dark cavern filled with writhing serpents. He encountered his greatest fear, Darth Vader. Having faced him and defeated him by decapitating the phantasm, Luke sees that his opponent was himself.
This encounter with the Dweller on the Threshold happened just before both Luke's and Rey's empowerment as Jedi. For Rey, a shadowy person approached the veil from the other side. Slowly the image cleared and Rey beheld herself. She was confused and angered at this, having expected the Darkness to answer her egoic questions. Here's something to remember: when the Force awakens within us, expect a somewhat demonic visitor.