Spoilers ahead for Star Wars: The Last Jedi. The latest Star Wars movie left audiences asking many questions that will hopefully receive answers with the next installment, Episode IX. That movie will come out in 2019, but director Rian Johnson, has given a few much-needed explanations to things like what the cave is in The Last Jedi, so not everything about the latest movie has to remain a mystery until the next Star Wars movie gets released. Two years is a long time to wait to find out who Rey's parents are or who Snoke is, but until then, Johnson's elucidations will have to be enough to tide Star Wars fans over.
Luckily, The Last Jedi's director doesn't hold back in explaining certain mysteries from the film, like what that dark under-water cave on the island of Ahch-To where Luke lived in Exile. In an interview with Slashfilm, Johnson said, "The idea that this natural place reflected […] that if there’s a Jedi Temple up top, the light, it has to be balanced by a place of great darkness." He continued to explain that Rey's finding of the cave resembles Luke's own past exploration of the Dark Side. "We’re drawing a very obvious connection to Luke’s training and to Dagobah here, obviously," Johnson said. "She descends down into there and has to see, just like Luke did in the cave, her greatest fear."
The scene in which Yoda leads Luke Skywalker to a cave resembling the Dark Side is a memorable one for all in Episode V: The Empire Strikes Back. In The Last Jedi, however, Rey finds the cave on her own, without Luke's guidance.
While Luke finds a projection of Darth Vader who turns into himself in Dagobah, Rey finds a mirror that reveals herself alone. Johnson explains this to Slashfilm, saying, "Her greatest fear is [that], in the search for identity, she has nobody but herself to rely on." Just as Yoda seemingly knows what Luke Skywalker saw while in the cave, Kylo Ren figures out what Rey's vision entailed, and he later uses that knowledge to manipulate her.
“They were nobody,” Kylo Ren tells Rey of her parents, according to the Daily Beast. The leader of the First Order continues, telling Rey, “They were filthy junk traders. Sold you off for drinking money. They’re dead in a pauper’s grave in the Jakku desert. You come from nothing. You’re nothing. But not to me.” Considering that Rey's greatest fears, reflected — literally — in the dark cave on Ahch-To, Kylo's harsh claims have a great effect on Rey, which leads audiences to wonder if she will end up joining the Dark Side.
Because of Kylo and Rey's intense connection throughout The Last Jedi, some fans have decided to ship a potential Reylo connection, though that seems unlikely with the ending of the latest film. Just as Luke both sees the Dark Side and leaves it to become a Jedi, Rey will most likely do the same. As Johnson explains, her interactions with the cave serve to demonstrate the power of the Force on Skywalker's island. "The idea was if the up top is the light, down underneath is the darkness," Johnson told Slashfilm.
Rey's interactions with the underwater cave may have seemed inconclusive — like many aspects of The Last Jedi — but it seems to have a great importance in connecting Rey to Luke Skywalker's story. Since Luke dies at the end of The Last Jedi, Rey might be the only hope for the Resistance since she has such a powerful connection to the Force. Seeing as her venturing into a cave resemble's Luke's, the chances that Rey will continue his mission of restoring balance to the galaxy seem high. Only time will tell, though — two years' time, to be exact.