Book II, Chapter VII
In order to discover the rules of society best suited to nations, a superior intelligence beholding all the passions of men without experiencing any of them would be needed. This intelligence would have to be wholly unrelated to our nature, while knowing it through and through; its happiness would have to be independent of us, and yet ready to occupy itself with ours; and lastly, it would have, in the march of time, to look forward to a distant glory, and, working in one century, to be able to enjoy in the next.  It would take gods to give men laws.
What Caligula argued from the facts, Plato, in the dialogue called the Politicus, argued in defining the civil or kingly man, on the basis of right. But if great princes are rare, how much more so are great legislators? The former have only to follow the pattern which the latter have to lay down. The legislator is the engineer who invents the machine, the prince merely the mechanic who sets it up and makes it go. "At the birth of societies," says Montesquieu, "the rulers of Republics establish institutions, and afterwards the institutions mould the rulers." 
He who dares to undertake the making of a people's institutions ought to feel himself capable, so to speak, of changing human nature, of transforming each individual, who is by himself a complete and solitary whole, into part of a greater whole from which he in a manner receives his life and being; of altering man's constitution for the purpose of strengthening it; and of substituting a partial and moral existence for the physical and independent existence nature has conferred on us all. He must, in a word, take away from man his own resources and give him instead new ones alien to him, and incapable of being made use of without the help of other men. The more completely these natural resources are annihilated, the greater and the more lasting are those which he acquires, and the more stable and perfect the new institutions; so that if each citizen is nothing and can do nothing without the rest, and the resources acquired by the whole are equal or superior to the aggregate of the resources of all the individuals, it may be said that legislation is at the highest possible point of perfection.
The legislator occupies in every respect an extraordinary position in the State. If he should do so by reason of his genius, he does so no less by reason of his office, which is neither magistracy, nor Sovereignty. This office, which sets up the Republic, nowhere enters into its constitution; it is an individual and superior function, which has nothing in common with human empire; for if he who holds command over men ought not to have command over the laws, he who has command over the laws ought not any more to have it over men; or else his laws would be the ministers of his passions and would often merely serve to perpetuate his injustices: his private aims would inevitably mar the sanctity of his work.
When Lycurgus gave laws to his country, he began by resigning the throne. It was the custom of most Greek towns to entrust the establishment of their laws to foreigners. The Republics of modern Italy in many cases followed this example; Geneva did the same and profited by it.  Rome, when it was most prosperous, suffered a revival of all the crimes of tyranny, and was brought to the verge of destruction, because it put the legislative authority and the sovereign power into the same hands.
Nevertheless, the decemvirs themselves never claimed the right to pass any law merely on their own authority. "Nothing we propose to you," they said to the people, "can pass into law without your consent. Romans, be yourselves the authors of the laws which are to make you happy."
He, therefore, who draws up the laws has, or should have, no right of legislation, and the people cannot, even if it wishes, deprive itself of this incommunicable right, because, according to the fundamental compact, only the general will can bind the individuals, and there can be no assurance that a particular will is in conformity with the general will, until it has been put to the free vote of the people. This I have said already; but it is worth while to repeat it.
Thus in the task of legislation we find together two things which appear to be incompatible: an enterprise too difficult for human powers, and, for its execution, an authority that is no authority.
There is a further difficulty that deserves attention. Wise men, if they try to speak their language to the common herd instead of its own, cannot possibly make themselves understood. There are a thousand kinds of ideas which it is impossible to translate into popular language. Conceptions that are too general and objects that are too remote are equally out of its range: each individual, having no taste for any other plan of government than that which suits his particular interest, finds it difficult to realise the advantages he might hope to draw from the continual privations good laws impose. For a young people to be able to relish sound principles of political theory and follow the fundamental rules of statecraft, the effect would have to become the cause; the social spirit, which should be created by these institutions, would have to preside over their very foundation; and men would have to be before law what they should become by means of law. The legislator therefore, being unable to appeal to either force or reason, must have recourse to an authority of a different order capable of constraining without violence and persuading without convincing.
This is what has, in all ages, compelled the fathers of nations to have recourse to divine intervention and credit the gods with their own wisdom, in order that the peoples, submitting to the laws of the State as to those of nature, and recognising the same power in the formation of the city as in that of man, might obey freely, and bear with docility the yoke of the public happiness.
This sublime reason, far above the range of the common herd, is that whose decisions the legislator puts into the mouth of the immortals, in order to constrain by divine authority those whom human prudence could not move.  But it is not anybody who can make the gods speak, or get himself believed when he proclaims himself their interpreter. The great soul of the legislator is the only miracle that can prove his mission. Any man may grave tablets of stone, or buy an oracle; or feign secret intercourse with some divinity, or train a bird to whisper in his ear, or find other vulgar ways of imposing on the people. He whose knowledge goes no further may perhaps gather round him a band of fools; but he will never found an empire, and his extravagances will quickly perish with him. Idle tricks form a passing tie; only wisdom can make it lasting. The Judaic law, which still subsists, and that of the child of Ishmael, which, for ten centuries, has ruled half the world, still proclaim the great men who laid them down; and, while the pride of philosophy or the blind spirit of faction sees in them no more than lucky impostures, the true political theorist admires, in the institutions they set up, the great and powerful genius which presides over things made to endure.
We should not, with Warburton, conclude from this that politics and religion have among us a common object, but that, in the first periods of nations, the one is used as an instrument for the other.
 A people becomes famous only when its legislation begins to decline. We do not know for how many centuries the system of Lycurgus made the Spartans happy before the rest of Greece took any notice of it.
 Montesquieu, The Greatness and Decadence of the Romans, ch. i.
 Those who know Calvin only as a theologian much underestimate the extent of his genius. The codification of our wise edicts, in which he played a large part, does him no less honour than his Institute. Whatever revolution time may bring in our religion, so long as the spirit of patriotism and liberty still lives among us, the memory of this great man will be for ever blessed.
 "In truth," says Macchiavelli, "there has never been, in any country, an extraordinary legislator who has not had recourse to God; for otherwise his laws would not have been accepted: there are, in fact, many useful truths of which a wise man may have knowledge without their having in themselves such clear reasons for their being so as to be able to convince others" (Discourses on Livy, Bk. v, ch. xi). (Rousseau quotes the Italian.)