First and foremost, the goal is to prevent the establishment of a Palestinian state. I would distinguish between the Israeli government's goals, though.
I mean, obviously they vary from time to time under different governments, but generally speaking, the goal in settling or colonizing the heart of the West Bank goal is to prevent the establishment of a Palestinian state.
As for the settlers themselves, they have a variety of goals. Obviously, for the most religious Zionists among them, it is to ultimately bring about the coming of the Messiah. However, I think the more secular goal is to prevent the establishment of a Palestinian state, and allowing the ongoing settlement is doing that, essentially. Every new settlement and every additional settler makes the establishment of a Palestinian state that much harder.