Between the Moral Law of God and the Civil Law of Man that is guided by Moral Law there is the other realm of law, which is Natural Law. This thing known as Natural Law are the boundaries that Nature places upon us, and in this I do not speak of the philosophical 'nature' (that is what are the characteristics of a thing or person) but the Universal Nature, which is the physical realm of the universe. This physical realm has two aspects to it: chaos and order.
Chaos is represented by the randomness of nature from the lowest levels, upwards. Brownian motion is bounded but chaotic in that it can have limitations upon it (based on volume, media type and temperature) but that what results in the way of motion is unpredictable at any given moment. Chaos creates randomness in events so that there is a factor of indeterminacy involved. This fact is part of Quantum Mechanics and comes from examining how Nature works.
Order is the sudden appearance of direction or higher order stability that resists chaos. The association of atoms in the form of molecules then has a larger scale set of predictable factors to them in the form of physical properties and structure. The capability for an underlying chaotic system to have structure appear is described by the concept known as emergence. When a number of unrelated factors then fall together into a new and unpredictable form of orderly behavior, then you have an emergent behavior that is unpredictable based on its component parts. All of this plays out in a framework within space and time, and these parts of the framework give rise to the effects we see. Part of that framework is chaos at the lowest most level and, from that, the framework will have chaotic things happen within it. Everything must cope abide by that at all other levels that coincide and derive from it.
Nature is, from that, chaotic and emergent to forms of order.
From this order is not the same as law, which makes law a separate realm from chaos, emergent behavior and order.
In Moral Law there is the requirement to acknowledge that we get it from something outside of ourselves and is a requirement for the Order of Man. Can Moral Law be described as an emergent phenomena? This would require answering the question: what is the source of the emergent phenomena? In the Universal sense this is God, that thing that all can know and yet none can fully define. Moral Law, recorded in scripture, also appears (in part) in other cultures as well that do not have scriptural basis for their Moral Law. What parts of this are Universal to Man? And why ask that question at all?
The reason for asking the question is that Man is a rational being (that is able to discern cause and effect, remember them and think about them dispassionately) and seeks to find those patterns that exist across different areas of knowledge to see if they are related. A positive relationship (that is an equivalence of pattern) then points to underlying structure with possible variations that can be examined as to their true universality. A truly Universal conclusion is true across all domains that are encompassed by the hypothesis, while a localized one is that which is true only for a locality. Thus for those things that Man finds across cultures that are equivalent, there can be some examination as to what the source of those qualities are.
The most Universal quality of man is this thing we do known as 'marriage' or the bonding of man and woman to create a family via intimate relationships. Marriage is seen across all cultures in some formulation and across all eras of mankind that we have records for. From that we can put the hypothesis down that marriage is a Universal quality for those beings that are capable of recognizing the need for such a bond and being able to assent to it in a voluntary fashion. Traditions of 'arranged marriages' through matchmakers or other venues is a cultural phenomena on top of the underlying structure of marriage and is created to turn a voluntary and yet wholly necessary need into a stable system of society that is involuntary. Those systems, then, are phenomena based on the underlying premise, not the underlying premise itself as, absent those social structures, the quality of Man to seek marriage would still exist.
To marry is to form a social unit called the family. Doing this then has other requirements with it to safeguard the family. The first of those is self-sacrifice on the part of parents for their children so that the children may survive to continue the lineage and social order of that family. This is not just a mother or father dying to save a child, but goes much deeper into us as individuals to address our negative natural liberties and rights. There is no such thing as a purely positive liberty or right: all liberties and rights are of two parts via Nature so that they are not biased and have no direction to them. By having natural liberty and rights in equal parts (though not, of necessity, equal amounts) chaos is guaranteed expression via both venues. To gain order from these natural rights and liberties requires an assertion of willpower over them when they are exercised. Thus to put aside negative natural liberty of, say, offensive warfare without cause then requires an expression of will on a continual basis by individuals to not use this negative right to exercise this negative liberty to put the family in danger.
Because this is of primary importance as warfare is lethal, it must be agreed upon by all family members and that agreement made specific and stated for all involved. From this we get this thing called Civil Law within the context of Law of Nations. Civil Law is nothing more than the assertion of will over our negative liberties in a way agreed upon by our fellow man so as to not exercise the natural rights associated with them and this adhered to by all with consequences for not following those agreements. The result of such Civil Law is emergent order from the society that is created by these agreements. Because such agreements need to be remembered in their specifics an organ of society known as government is created to be the holder of these agreements about our negative natural liberties. Although there is a Moral Law of 'Thou shall not kill', which is part of a formulation of creation of Civil Law, this is understood to be in the realm of Moral expression in the Civil arena. There is no 'Thou shall not go to war on your lonesome' edict and, indeed, there are individuals that find themselves doing just that without moral or civil justification for their acts. Such individuals have decided not to follow Civil Law under Law of Nations and reclaim their full natural liberty and rights for themselves and are now in opposition to those who follow Civil Law which is part of this thing known as Civilization. This is a reversion to base savagery against civilization, a return to natural man who is full of chaos and unwilling to assert will to get a social order.
Law is the creation of order via the assertion of will and the restraint of use of negative natural rights and liberties. This is true of Law of Nations, that law created by marriage, and for Civil Law, that law that comes from the creation of society for protection amongst families and for family members within the family unit. Moral Law is a bias or direction to Natural Law which itself is without bias and equal in treatment to all within it. Man cannot make Natural Law because we live within Nature and are natural beings. Man can find or have revealed Moral Law as it is that which is outside the realm of Nature, outside the realm of thought and wholly within the realm of the Eternal but can be expressed within the Natural realm.
From these things we find the following Laws:
1) Moral Law can be discovered via revelation or via chance (such as social groups finding that the punishing of those killing within that social group requires a cost to that action to deter it). As such the foundations for a moral outlook are Universally available, although the pathway to that understanding can be indirect as well as direct. If you do not have revelation, then you have trial and error using rational observation to see what the results are for certain action and re-action pairings.
2) Natural Law acts upon all things in Nature and is universal within the realm of Nature. Being within this domain of law means we do not set it, do not create it, and it exists wholly outside of our sphere of influence, Nature provides us with our bodies, our lives, and the physical world which we can manipulate. Nature is uncaring, neutral, and provides much in the way of the physical domain that we don't understand and may never be able to understand.
3) Law of Nations is the unwritten law that Man discovers via the application of Moral Law to oneself for the creation of family. Law of Nations is universal to all thinking beings who have access to Moral Law, which is to say all rational beings that procreate and create families via a bond of marriage or other, similar, dedication. This exists not just within the confines of Natural Law but as a concept separate from Natural Law, making Law of Nations Universal to all rational beings.
4) Civil Law is created by society which, itself, is made under Law of Nations, and is the expression of Moral Law within Law of Nations by a society which wishes to create a State for safeguarding the population against those who would express their negative natural rights and liberties against their fellow man. Moral Law gives founding to direction and bias on those Natural liberties and rights that we have, and when we create a family we find that Moral Law almost immediately from being Natural Beings who must protect our offspring from Nature's creatures that do not so well discriminate their negative liberties and rights than do we.
When man has no ability to write, indeed has no alphabet but does have a spoken language or other means of communication, items from the realms of unwritten law become an integral part of the communication's tradition so that it may be passed on and preserved. Moral Law can be revealed and passed down by word of mouth, Natural Law is always present to present questions and get results and those results are reflective of Nature, Law of Nations to protect family and create the Nation is universal upon first creating family and its form becomes apparent because of that. Civil Law is the last law that is derived from the other laws and it, too, can exist in an unwritten form as a set of customs or practices that those within a given society live by.
There are interesting aspects of Moral Law in this arrangement, in that it is not (of necessity) written down but can be discovered by Man who utilizes both emotions and reason, together, to find answers to problems that arise in society. Law of Nations is that which is about structure, duty, and ordering of power by society due to it being a society and interacting with other societies that hold different customs. Before revelation man utilized chance, which is to say trying things differently until finding something that worked, to deal with problems created between men within society. Law of Nations can only speak of this as a manifestation within society that is stable, it cannot say what Moral Law is but that it is a formulary necessary for Law of Nations to happen fully.
By staying one's hand within a family, by not killing each other, by not stealing from each other, indeed, by not inflicting lasting harm upon the family the expression of Moral Law becomes visible: it is that which guides us on how to create a stable family and society. This requires both reason (as understanding that harming a family member will rebound negatively on oneself) and emotion (to understand that forgiveness for the faults of family members is necessary to have a family, but that forgiving only comes with the atonement by that individual that did wrong by the family). That same staying and continued withholding of it creates the family, as well. When spouses are abusive to their mate, their children or themselves, there is a fundamental violation of Moral Law, and as it is destructive to Law of Nations it is a negative factor for having Nations and even civil society. That is why we have Civil Law so as to penalize such activities and safeguard families from abusive parents: it is to transmit that the family order has a reason behind it, a rationale, that it is positive when upheld and negative to not just the family but the Nation when it is neglected or abused. To not punish these actions by actors is to invite the decay of society and the downfall of it and the Nation that is sustained by the family. Penalties in this realm have been severe on the Civil Law side and for Natural Law the ability to protect oneself and one's family invokes the positive liberty and right of warfare: defensive war for survival and self-protection.
From all of this there are interesting questions that can be posed in the context of Universal Laws, but they are more of interest to philosophers or theologians than to those surviving a daily life. That we can even formulate such questions is a testament to the power of these Laws and that our holding to them can create a long lasting society and the concept of Nation even when Nation States rise and fall many times in the same region.
The actual ability to even ask those questions has required that there be tolerance for asking them, and that has been a high powered, long fought after battle that has spanned nearly all of human history, was first given any written establishment for Nations in 1648, and is still NOT recognized by large swaths of mankind and is being actively fought against within those areas that have it. Yet religious tolerance has become an instance of the highest order of civilization so long as a religion does not dictate to the State and only to the individual, and that society remains open to other religious beliefs that do not seek to impose themselves by negative natural rights and liberty. That is an effect of how a fight for aspects of Moral Law that have the same basis has established a common space for those religions to exist in a secular realm. The secular realm, itself, must be open to religious teachings of all religions that follow the same civil principles of respect and tolerance for believers of other faiths.
To try and exclude Moral Law as garnered by religious faith from the secular space is destructive to that space as it undercuts its very existence: to find commonality across beliefs that can be upheld without imposition of any particular faith upon those who do not believe in it. By holding commonalities to be common requires the robust and civil discussion of Moral Law within that secular space so that better Civil Laws can be found. Do note that even atheists, agnostics or those who civilly practice relatively unusual religious rights are not the holder of this secular space, but participants in it. Those who do not believe in religious basis for the underpinning of the secular space must recognize the origins of that space, their protection within it as a higher form of learning and that, in particular, if it is garnered via mere trial and error via faiths, then it is more precious than any single faith within that realm and therefore MUST be upheld as a neutral space for such civil discussions.
Secular space for government does not mean that such government does not recognize the foundation of the secular space or those things necessary to uphold it: indeed it was formed to protect those practices, not expunge them.
Secular space for society is a recognition and acceptance amongst all members of society as individuals that their practice of faith (or lack thereof) may not put the civil basis for society at risk without penalties and that their ability to practice a faith and even change faiths is upheld by having a neutral secular space that is common for all of society. What you do with your life and within your household shall not undercut that common space that must be open to all arguments and that arguments on Moral Law must first be won by civil discourse, not by secular fiat or by gaming government practices. Indeed when government becomes biased to exclude Moral Law and its teachings from the secular space, or to only allow a delimited set of discussions via civil means, it becomes destructive of the entire society that creates that secular space for religious freedom. The worst of all tyrannies is government deciding which religion is and is not acceptable within the civil sphere and then using the power of government to enforce that. When the State comes to mandate its presence upon the alter, you are then not far away from open warfare as this is a desecration of the advanced civilized understandings of tolerance for religious worship and practice within realm of civil society.
By utilizing the understandings of Laws Natural and those outside of Nature (although available within Nature) and then adding historical understanding of practice and conflict of many Nations, States and societies, the foundations of the framework for the modern world lay exposed and available to all willing to see them. Even if you disagree with how they got there or deny the impetus to make them, the recognition of the self-evident presence of it must be admitted: argue about the source of the foundations as you will, we must accept that they exist, have instance and are there.
To not do so is to invite the decay and collapse of civilization as we know it and to seek savagery not only for oneself but for all of mankind. No good will ever come of that.