First, a quick definition of so-called "natural law": it is epitomized in Kant's categories of understanding, which, translated, = categories or conditions that shape and determine human awareness and understanding.
In other words, there's no "matrix" or escape from the Platonic Cave.
In more technical-speak, there are inherent processes in nature, physis, that evince and define "what is the good?"
Saint Thomas Aquinas' perspective on natural law is Biblical--God reveals morality in Nature. So the "central element" or essence of Aquinas' perspective is that law is "...nothing else than an ordinance of reason for the common good, made by him who has the care of the community..." (Question 90, "Of the Essence of Law"). This "him" extends, Jacob-ladder-like, up to the Creator and the heavenly hosts. In other words, Saint Thomas Aquinas affirms that there is way out of the dense human matrix, and the Cave dwelling darkness.