It is this: the PLO is the only Palestinian organization that can negotiate with Israel, and Hamas won't stand in that way. But any agreement reached in those negotiations has to be ratified by a referendum. There is no need for Israel to negotiate with Hamas, because Hamas has said it would abide by any agreement that has been ratified by such a referendum. Clear enough?
U.S.-led coalition stages 41 airstrikes on ISIS targets in Syria and Iraq - joint command (Reuters)
from the article: Abu Mazen wants a state, not the right of return