Fate paired Rey and Finn together in Star Wars: The Force Awakens...or maybe it was the will of the Force. Regardless, the circumstances of them meeting each other on Jakku were extremely hectic. Finn was a guy running away from the First Order, while Rey was patiently waiting for her family to find her on that desert planet. Thanks to BB-8 and great timing, they crossed paths and eventually built a close friendship. However, according to director J.J. Abrams, in an earlier draft of The Force Awakens' script, their first meeting had more edge to it.
Originally, they were much more angry at each other, and truthfully it wasn't working. Originally in this scene, Finn revealed that he was a stormtrooper. And in this scene, she had never heard of Luke Skywalker, which didn't really make sense, because later, she's heard of Han Solo, and she's been wearing the Rebellion helmet, you just didn't quite buy it. But the idea was that her life was so isolated, so sad, so without hope, that the most optimistic thing, that was Luke Skywalker himself, was nothing but a Myth. And the idea is that Finn brings this hope to her. Also this really fun concoction that Finn is lying to her, that his truth that he's actually a stormtrooper is covered up by this lie that he's with the Resistance. That allows for Daisy to sort of fall for this guy that's this daring, brave, good man, but of course he's lying. And she's so lost in her own life that when she hears the name of Luke Skywalker here, she doesn't even believe it's real.
J.J. Abrams is correct on both points. Starting off, having Finn immediately reveal he was a stormtrooper to Rey would have been a weird move, as that would have eliminated his attempts to deceive her about his past. Not in a malicious way, but simply because he didn't want her to judge him because he used to serve the First Order. Plus, if he hadn't pretended to be part of the Resistance, Rey and BB-8 might not have let him come along on their journey after escaping those TIE Fighters.
As for Rey originally not knowing about Luke Skywalker, that's wouldn't have made any sense at all! Yes, she never ventured off the desolate Jakku, but how can you have heard about Han Solo, but not know who Luke Skywalker is? That's the man who destroyed the first Death Star, led the defense of Echo Base, fought Darth Vader twice, etc. Thankfully that plot issue was also remedied, and in the end, Rey found Luke Skywalker on Ahch-To to return his old lightsaber to him. Now she's learning the ways of the Force from the aged Jedi Master.
Rey and Finn will return to the big screen when Star Wars: Episode VIII is released on December 15, 2017.