The background to Hawthorne's understanding of natural law is both classical and Christian. In the fifth century, philosophers and sophists distinguished between "physis" or "nature/natural law" and "nomos" (convention, human law). Gravity is natural law; law codes forbidding stealing, murder, adultery, or running red lights are human laws. A major philosophical question was that of (1) where the boundaries were between nomos and physis (are laws against incest or murder conforming to nature and universal or just local custom?) and (2) whether nomos should imitate physis (is nature a good model? or is the purpose of convention to tame brutish natural instincts?) Hawthorne, as all people of his period was classically educated and aware of this debate.
In Christianity, there is the notion of God having written two books, the Liber (Bible) and Liber Mundi (book of the world), both intended to reveal his mind and will to humanity. If nature is God's creation and human law the creation of fallen humanity, then the natural order is superior to "man's law."