This is my personal opinion,so feel free to prove me wrong :D
In SW-ANH,Obi-wan tells Luke that "all life is connected to the Force".Later,after the destruction of Alderaan,he says something along the lines of "I felt a distubance in the Force,as if millions of souls cried out in terror".So,it's clear that emotions are transmitted through the Force.
If enough people feel "good" emotions(love,happinessand so forth)the nature of the Force could swing towards the Lightside;and conversely for "dark" emotions.Either extreme is undesirable as people need both kinds to function properly.So,if the Force swings to one extreme,it works through Force sensitives to bring it back into balance,eg Anakin Skywalker destroyed the Jedi Order.Unfortunately he went too far and brought the Dark Side into dominance,and so the Force was required to work through Luke,bringing the Force into balance again,in what is probably a never ending cycle.
Interestingly,I was intending to say that the Force doesn't have a will,but now I'm thinking otherwise.It must be the Force working through me "