The 'Lighter' Side Of The Force
If Kylo Ren is having to fight off the light side it says to me that the light has more of a pull on him then we think and Rey helps him turn to the light after she becomes aware that he is family and for Luke, he has become so powerful in the force that he is scared of what his powers could do and from the looks of him and the look he gives Rey at the end of The Force Awakens says to me he will turn to the dark side and both Rey and Kylo Ren " Ben Solo," end up in a battle with Luke.
Kylo Ren isn't a Sith in the first place. And yes it does seem a lot like Harry Potter. Great theory! Personally I hope he doesn't turn good. I hope he dies a bad guy, or kills everyone good with few remaining
Luke set this whole thing up.He knew they needed someone on the inside and in Rey's vision of Luke touching R2-D2, Luke is watching the Jedi Academy go down.Luke touches R2 to comfort him. Only Vader ever got close enough to take down Palpatine. Now eventually Rey will be trained by Luke and Luke and Rey will have an epic lightsaber battle vs Kylo and Snoke in Episode IX where Kylo flips and its a 3 on 1 battle. Skywalkers and a Solo taking down the last ever Dark Lord and thus bringing peaceful balance to the Force.
Finishing what Vader started he means when Vader took down the Emperor and didn't succeed him at the new Dark Lord. Vader started but never finished the destruction of the Empire, now the First Order.