I've always ignored the prophecy, making my own twist of the SW Universe saying that the Force is always in balance... but that's just me. But because I feel like it, I'm going to explain. I think there was no "Chosen One" or one that was supposed to have brought balance to the Force. Instead, no matter what happens, niether side can be wiped out completely, and won't be gone long. Both sides are always at the same potential strength. So, when Luke was the only remaining Jedi, he needed enough power to balance against the other two. So he had the potential to get it, and through the movies found it... saying that either means that his actions led to the death of Palpatine or that he found added strength in his father... either way. But that makes the Force almost seem sentient, almost like a god throwing elements together and enjoying the show.