I think, personally, I'd prefer the prophecy not to have a huge direct impact on events. It's more fascinating to me how it might drive the story by its mere existence as people's behaviour and reaction to it can cause them to do things that leave a heavy mark on the world, maybe even a self-fulfilling prophecy in a way, and some people might scorn its validity. In terms of drawing everyone together it could be that a lead draws them to the same place... the other possibility might be that 'someone' has that lead but knows they will need help, so reluctantly tries to call others together, and a band of missfits is created. It might be worth talking characters to work out how best to fit them together.