First, let's assume Rey is the ST parallel to Luke (even though she's an amalgamation of Luke and Han, much the same way Ben is.)
There are three instances where Luke uses the Force in the OT with no real practice, much like how Rey doesn't have real practice.
- Luke guides the torpedoes into the Death Star. (It's also established that he can shoot wamp rats in Beggar's Canyon, so we know he's semi-capable.)
- Luke Force communicates with Leia on Bespin. (Although we could headcanon that Luke learns to Force communicate between ANH and ESB.)
- Luke Force grabs the Skywalker legacy saber in the wampa cave with no prior training. (Again headcanon he learns this between ANH and ESB.)
Luke and Anakin and Rey and Broom Boy are all Force sensitive. It's super established in canon and specifically in the films you don't need training to be Force sensitive. (You need a high count of Force sensitive microbiology in your blood, according to Qui-Gon anyway.)
We also learn from Yoda in TPM that Force sensitive people (space people) connect through the Force through their emotions. "Fear leads to anger, Anger leads to hate, hate leads to the BLAH BLAH to the dark side."
Luke reemphasizes this fact to Rey on Acht'To.
So Luke trusts in himself and the Force and blows up the Death Star with the Force with no real Force training.
Then Luke gets his ass handed to him and his hand ✋ cut off in ESB. He's hanging on a poll on literally his last limbs. Suddenly he can reach out and Force communicate with Leia and she returns with the Millenium Falcon to save him. This is after Yoda tells him about the rocks and how there is No Try Only Do. So he only "DOs" and communicates with Leia. Sure Luke got Force training from Yoda, but (at least on camera) he never learns how to Force communicate. But when he desperately needs to, he can. Desperation is what I think is the emotion that taps him into the Force here.
And before Luke meets Yoda he's able to Force grab the Skywalker legacy saber in the wampa cave with zero experience, zero training because that's what he needs in the moment and he's Force sensitive.
Now Rey! So Rey is Force sensitive and it's super established she's had to protect herself with her melee weapon, her bowstaff, on Jakku. She's ten times more capable at melee combat by the time she's 12 than Luke has ever been ever.
Ben kidnaps her and pries into her mind. Here she is desperate and she can feel Ben inside her mind. In her desperation she is able to fight him back. He's already in her mind with the Force, it makes sense that she would feel what he's doing and fight back. This happens to Poe earlier in the film, but he's not Force sensitive, he can't push back through his emotions. She feels him in there and is able to fight back a little. She starts reading his mind his fears, since those are the darkside emotions he's using to connect to the Force and enter her mind. "You're afraid you'll never be as strong as Darth Vader." Ben, obviously more powerful with the Force than Rey, again having honed it with his dark emotions cuts her off from his mind immediately.
Fast forward to Rey cuffed to the chair, Stormtrooper007 walks in. She tries a Jedi Mind Trick. It doesn't work, she tries again, truly focuses and it works. Now Ben was just in her mind and because of that she was in his mind. So a Jedi Mind Trick is just an extension of what she learned at that moment of pushing back into Ben's brain. It's not that she learned the Jedi Mind Trick from his mind, she didn't download this information, it's that a Jedi Mind Trick is a natural extension of punching back into Ben's mind. In many ways it makes more sense that she can do this at this moment, more so than Luke using the Force to guide the torpedoes or tapping into Leia's mind on Bespin. Luke has never had someone enter his mind, although if he did he'd probably be able to push back slightly and be like, "Oh, I understand how to enter a mind with the Force since it's happening to me."
Again, she doesn't download the ability to Jedi Mind Trick, it's simply an extension of what she learned when she fought back against Ben entering her mind. It's never stated in canon how long it takes to perfect a Jedi Mind Trick, in fact it's never really established how long it takes to perfect any connection to the Force. I assume that it's different for everyone. For Broom Boy it's easy to Force grab the broom. Did he practice this for years? Probably not, he's just Force sensitive and that's what he emotionally wants at that moment, so he's able to connect to it. Same with Luke with the torpedoes and with the Leia communication and when he grabs the Skywalker legacy saber in the wampa cave.
So now that brings us to the Skywalker legacy lightsaber going to Rey and not Ben. In TLJ, they break the saber in two, meaning they are now in fact equals in the Force. But in TFA, the Skywalker legacy saber calls to Rey. This is simply because she's Force sensitive. Not sure why when Luke touches the saber in ANH he doesn't get a Forceback but maybe it's because he's never really supposed to have the Skywalker saber as is evident in it being chopped off with his hand ✋ by the original owner of said saber. And then even more evident when he throws it away in TLJ (Like how he throws his green saber away when he refuses to fight his father anymore and give into his anger in RotJ).
So Ben kills his dad and then gets shot in the gut by his Uncle Chewie. He then easily fights off Finn, who's shitty at handling a melee weapon, and then Ben attempts to grab the Skywalker legacy saber with the Force, but it's clear that emotionally Rey wants it more, and she's also not bleeding into the snow, so it comes to her and the crowd in the theatre cheers. And he fights Rey. And it's sloppy, trees fall, lightsabers scrape across the snow, it's not the elegant Jedi lightsaber battles we've seen in the PT, it's messy.
He then has the upper hand on her, sabers crossed, then he reveals he's been holding back, "I can teach you the ways of the Force," he says. She then closes her eyes, similar to Luke putting his cross hair visor up before launching the torpedoes into the Death Star. And she knocks down a Ben who just refused to kill her, who wanted to train her instead.
So throughout TFA I don't believe Rey downloaded anything from Ben's brain. She fought back against his brain intrusion, then was able to intrude into Stormtrooper007's brain. She is able to Force grab the Skywalker legacy saber because A. Ben is at a weakened state at the moment, B. He's just killed his father, his emotions are out of whack, C. Rey's emotions are not out of whack, they are super focused. She's then able to defeat him because A. He's hurt both emotionally and physically, B. He doesn't actually want to kill her. C. She has mad melee weapon skills which a tiny bit carried over believably from bowstaff to saber.
Now onto TLJ, Rey is trained by Luke in the fallacies of the Jedi. He teaches her different than he taught Ben intentionally so the PT/OT way of the old Jedi will die. This is one reason why Luke is the Last Jedi of old.
He taught Ben how to be a Jedi and hold in his love and anger and it failed much in the same way it failed Anakin.
Now according to Snoke, he bridged the minds of Rey and Ben to trick them into the Throne Room so he could finally get the info of where Luke is and kill Luke. This could be a lie, the connection could've been established the moment Ben entered Rey's brain in TFA. We don't really know, as the connection is still present after Snoke dies. We also know that when Rey trains herself in lightsaber fighting, as Luke refuses to teach her how to fight since a Jedi fighting he believes is what led to the rise of Darth Sidious and the destruction of the Republic, she has the same moveset as Ben. Now they already fought, so she knows how he fights, they've also been Force communicating and have penetrated each other's minds in TFA, so this is the only thing that I can see believably being downloaded into Rey from Ben and it's insignificant, it's really an Easter egg that they have the same move set that people out together on the internet. It's really cool, but it's not too important to the plot or even character development that they have the same fighting style.
Anyway we learn that Ben has equal light equal darkness in him as evidenced by him killing his father but then feeling remorse, him saying to his grandfather's helmet that he feels the pull to the light and when he can shoot and kill his mother but not only decides against it, he actually shoots and kills his wingmen who shoot and blow up the command bridge Leia is on. Luckily his mom is Force sensitive so she's able to pull herself into the ship saving her life. Then we have Rey who we think is only lightside good, which she proves when she doesn't trade in BB-8 for a bunch of portions of food. But then we learn she has intense darkness inside of her which Luke says is equal to Ben's darkness, "I've only seen this type of darkness once before, in Ben Solo" (I think I butchered the line). And then they split Excalibur... I mean the Skywalker legacy lightsaber perfectly in two with their equal Force powers. They are certainly the balance that the prophecy was foretelling.
So here's the final thing: What do the Jedi perfect with the Force and learn as Jedi? Well they learn how to hone their emotions into the Force. They are monks who learn not to give into their dark emotions and utilize their light emotions to connect to the Force. Once Luke perfects his connection to the Force we see that he's learned how to disconnect himself from the Force which probably takes a lot more effort than a Jedi Mind Trick or Force Pull/Grab. We then see Luke do something we've never seen another Jedi do, and that's not only Force project (or as I like to say "skywalk" across the Galaxy) but also he becomes one with the Force in a greater way than we've ever come across, greater than Obi-Wan or Yoda or even Anakin, he truly becomes The Last Jedi of the PT/OT Jedi way. What we see Luke do is the stuff Jedi train years to perfect (perfecting projecting). Utilizing the Force in the magnitude he did is what Jedi train their entire lives to do.
- Chris "ZeitChrist" Taylor