What is the difference between a government of force and a government of law?

Think of a policy as a plan. We will do B if A happens. The best example I can think of is the policy that the United States does not negotiate with terrorists. That is a policy, but it has been broken, for example, when POW were traded from Guantanimo Bay for US soldiers taken hostage. 

A law is legally binding. For example, the President of the United States can veto bills. That isn't a policy. The President doesn't have a guideline that he can veto bills and Congress can't say we will break that "policy" this time. That is the law so they must allow it. 

In short, policies are not legally binding. They are "plans". 

Laws are legally binding. They are final and concrete, for the purposes of this discussion.