This then is the general signification of law, a rule of action dictated by some superior being: and, in those creatures that have neither the power to think, nor to will, such laws must be invariably obeyed, so long as the creature itself subsists, for it's existence depends on that obedience. But laws, in their more confined sense, and in which it is our present business to consider them, denote the rules, not of action in general, but of human action or conduct: that is, the precepts by which man, the noblest of all sublunary beings, a creature endowed with both reason and freewill, is commanded to make use of those faculties in the general regulation of his behaviour.
Man, considered as a creature, must necessarily be subject to the laws of his creator, for he is entirely a dependent being. A being, independent of any other, has no rule to pursue, but such as he prescribes to himself; but a state of dependence will inevitably oblige the inferior to take the will of him, on whom he depends, as the rule of his conduct: not indeed in every particular, but in all those points wherein his dependence consists. This principle therefore has more or less extent and effect, in proportion as the superiority of the one and the dependence of the other is greater or less, absolute or limited. And consequently, as man depends absolutely upon his maker for every thing, it is necessary that he should in all points conform to his maker's will.
This will of his maker is called the law of nature. For as God, when he created matter, and endued it with a principle of mobility, established certain rules for the perpetual direction of that motion; so, when he created man, and endued him with freewill to conduct himself in all parts of life, he laid down certain immutable laws of human nature, whereby that freewill is in some degree regulated and restrained, and gave him also the faculty of reason to discover the purport of those laws.
Considering the creator only as a being of infinite power, he was able unquestionably to have prescribed whatever laws he pleased to his creature, man, however unjust or severe. But as be is also a being of infinite wisdom, he has laid down only such laws as were founded in those relations of justice, that existed in the nature of things antecedent to any positive precept. These are the eternal, immutable laws of good and evil, to which the creator himself in all his dispensations conforms; and which he has enabled human reason to discover, so far as they are necessary for the conduct of human actions. Such among others are these principles: that we should live honestly, should hurt nobody, and should render to every one his due; to which three general precepts Justinian has reduced the whole doctrine of law.
But if the discovery of these first principles of the law of nature depended only upon the due exertion of right reason, and could not otherwise be obtained than by a chain of metaphysical disquisitions, mankind would have wanted some inducement to have quickened their inquiries, and the greater part of the world would have rested content in mental indolence, and ignorance it's inseparable companion. As therefore the creator is a being, not only of infinite power, and wisdom, but also of infinite goodness, he has been pleased so to contrive the constitution and frame of humanity, that we should want no other prompter to inquire after and pursue the rule of right, but only our own self-love, that universal principle of action. For he has so intimately connected, so inseparably interwoven the laws of eternal justice with the happiness of each individual, that the latter cannot be attained but by observing the former; and, if the former be punctually obeyed, it cannot but induce the latter. In consequence of which mutual connection of justice and human felicity, he has not perplexed the law of nature with a multitude of abstracted rules and precepts, referring merely to the fitness or unfitness of things, as some have vainly surmised; but has graciously reduced the rule of obedience to this one paternal precept, "that man should pursue his own true and substantial happiness." This is the foundation of what we call ethics, or natural law. For the several articles into which it is branched in our systems, amount to no more than demonstrating, that this or that action tends to man's real happiness, and therefore very justly concluding that the performance of it is a part of the law of nature; or, on the other hand, that this or that action is destructive of man's real happiness, and therefore that the law of nature forbids it.
This law of nature, being coeval with mankind and dictated by God himself, is of course superior in obligation to any other-It is binding over all the globe in all countries, and at all times; no human laws are of any validity, if contrary to this: and such of them as are valid derive all their force, and all their authority, mediately or immediately, from this original.
source: Commentaries on the Laws of England, Book I, Section 2