Rey's training montage in Star Wars: The Last Jedi actually foreshadows the climactic battle between Luke and Kylo Ren. It may also offer insight into one of the film's key plots; the strange, twisted relationship between Kylo Ren and Rey.
Star Wars Episode VIII has proven to be remarkably divisive. While the critics overwhelmingly loved it, a vocal number of Star Wars fans were irked at certain plots and themes. But there's one thing even the film's harshest critics have to admit; stylistically, The Last Jedi is absolutely beautiful. Director Rian Johnson worked hard to create a film that was lovingly rendered in almost every way; Star Wars: The Last Jedi has a remarkable, stylized feel to it that just begs for deeper analysis.
Over on Reddit, one fan has spotted a beautiful moment of foreshadowing. Early on in the film, there's a scene in which Rey trains with the Skywalker lightsaber, sweeping the shimmering blade around a rocky outcrop. Not only is Rey testing her lightsaber style, she's also assessing her own self-control. And she ultimately fails, slashing into the rock, chopping the top off it. Luke, needless to say, is not impressed. It's an effective scene, but it actually carries a lot more weight than viewers realized at first glance: Rey's practiced moves are almost identical to the ones Kylo Ren would use against Luke at the end of the film.
While this is tremendously effective in terms of foreshadowing, it's also quite an important detail. Star Wars: The Last Jedi implies that Rey and Kylo Ren together bring balance to the Force. Rey, although tempted by the darkness, commits to the light; Kylo Ren, beckoned by the light, instead chooses darkness. The film goes to great lengths to show Rey and Kylo Ren as equal and opposite, and this is another subtle way of demonstrating that.
But it may actually be a smart plot-point as well. In Star Wars: The Force Awakens, Kylo Ren attempts to use the Force to access Rey's mind. Rey resists, and instead sees into Kylo Ren's mind. That's the moment when a psychic bond is created between the two, and a popular theory is that Rey's subconscious mind absorbed a great deal of Kylo Ren's knowledge of the Force; that's how she was able to beat him in a lightsaber duel later on in The Force Awakens. This training montage may hint that the theory is right and that Rey has absorbed knowledge of Kylo Ren's own fighting style. If so, the fact Luke watches with concern and a hint of disgust becomes even more significant.
It's also worth remembering that this training scene happens partway through the film. The bond between Rey and Kylo Ren has been encouraged by Snoke, and the two have already begun to have troubling visions of one another. Jason Fry's novelization establishes that each vision led to the bond between Rey and Kylo Ren becoming deeper, with knowledge of the Force seeping into Rey's mind:
"She had seen more - far more. Somehow, almost instinctually, she knew how he accessed some of the powers at his command - even though she didn't understand them. It was as if his training had become hers, unlocking and flinging open door after door in her mind."
No wonder Rey's fighting style is becoming reminiscent of Kylo Ren's. She's only trained with a lightsaber for a week at most; he's had a lifetime, and all that knowledge and discipline has been absorbed into Rey's own skillset.
As controversial as Star Wars: The Last Jedi may have been, scenes like this underscore the efforts of Rian Johnson. He's performed a remarkable feat, creating a Star Wars film with an unusual level of depth and symbolism to it. In this case, a single training montage - easily viewed as just a cool moment - carried unexpected depths of meaning.