The Second Pillar - The Rule of Law
One of the ways the first pillar, property rights, is guaranteed is through the Rule of Law. To the extent that the power of society will be used to guarantee your right to property, it makes that right meaningful.
Rule of law serves other purposes, as well.
It helps to set common expectations of what you must do, what you may do, and what you may not do. In setting these expectations, it serves as an codified expression of societal values, and helps define the relationship between the state and the individual, and illustrates the society's attitudes toward both liberty and responsibility. The law's scope and extent in a society reflect a great deal about its culture and beliefs.
'Good' rule of law requires well considered meta-law - what are the rules for how laws will be made, enforced, administered, and changed?
If rule of law is truly in effect, then actions can be evaluated against known objective standards, rather than by the whims of individuals with personal power and influence. The more reliably you can tell prospectively whether a considered action will be 'lawful', rather than needing the judgement of a court after the fact, the more effective is the rule of law.
Rule of law can be effective (or ineffective) in a wide variety of societies, using a variety of systems of government - but much of a government's effectiveness can be judged by its attitude toward the law.