Since this is a digest of his very long work (which I kind of want to read), it doesn't have the kind of sustained argumentation I was hoping for. But all the same, it is a very coherent exposition of principles of natural law that are still largely consistent with Western mores three hundred years later. We still consider it necessary for everyone to abide by agreements and organize mutual defenses against human aggression.
"Natural law" is the phrase used in Pufendorf's age to refer to principles of morality that hold for all possible societies and that is known through reason. It is contrasted with divine law, which is known by special revelation, and civil law, which can be formulated in one way or another at the discretion of a sovereign. (I tend to think that they called it "law" mostly by analogy with those other two categories. So it's not surprising that a decline of interest in the substance of ecclesial law was accompanied by a decline in interest in the term "natural law.")
I admire the effort to describe certain principles of human morality that are constant across time and cultures, and I think this kind of thinking deserves to be preserved even where the imaginary of "law" loses it salience. Excepting his tendency to assume that human social institutions are formed by agreement and not by status (plenty of cultures are way more status based than that of modern Europe and this raises questions about whether a more general account of status relations than Pufendorf offers would be appropriate for natural law) it's not as easy as one might think to find clear ethnographic counter examples to most of the moral principles that Pufendorf outlines. One doesn't have to read Pufendorf specifically, but I think some exposure to the natural law tradition is valuable. I would personally recommend the intro to Grotius' Law of War and Peace over this digest.