Book 1, Chapter 7: The Sovereign explained simply

CHAPTER VII THE SOVEREIGN This formula shows us that the act of association comprises a mutual undertaking between the public and the individuals, and that each individual, in making a contract, as we may say, with himself, is bound in a double capacity; as a member of the Sovereign he is bound to the individuals, and as a member of the State to the Sovereign. But the maxim of civil right, that no one is bound by undertakings made to himself, does not apply in this case; for there is a great difference between incurring an obligation to yourself and incurring one to a whole of which you form a part. Attention must further be called to the fact that public deliberation, while competent to bind all the subjects to the Sovereign, because of the two different capacities in which each of them may be regarded, cannot, for the opposite reason, bind the Sovereign to itself; and that it is consequently against the nature of the body politic for the Sovereign to impose on itself a law which it cannot infringe. Being able to regard itself in only one capacity, it is in the position of an individual who makes a contract with himself; and this makes it clear that there neither is nor can be any kind of fundamental law binding on the body of the people--not even the social contract itself. This does not mean that the body politic cannot enter into undertakings with others, provided the contract is not infringed by them; for in relation to what is external to it, it becomes a simple being, an individual. But the body politic or the Sovereign, drawing its being wholly from the sanctity of the contract, can never bind itself, even to an outsider, to do anything derogatory to the original act, for instance, to alienate any part of itself, or to submit to another Sovereign. Violation of the act by which it exists would be self-annihilation; and that which is itself nothing can create nothing. As soon as this multitude is so united in one body, it is impossible to offend against one of the members without attacking the body, and still more to offend against the body without the members resenting it. Duty and interest therefore equally oblige the two contracting parties to give each other help; and the same men should seek to combine, in their double capacity, all the advantages dependent upon that capacity. Again, the Sovereign, being formed wholly of the individuals who compose it, neither has nor can have any interest contrary to theirs; and consequently the sovereign power need give no guarantee to its subjects, because it is impossible for the body to wish to hurt all its members. We shall also see later on that It cannot hurt any in particular. The Sovereign, merely by virtue of what it is, is is always what it should be. This, however, is not the case with the relation of the subjects to the Sovereign, which, despite the common interest, would have no security that they would fulfil their undertakings, unless it found means to assure itself of their fidelity. In fact, each individual, as a man, may have a particular will contrary or dissimilar to the general will which he has as a citizen. His particular interest may speak to him quite differently from the common interest: his absolute and naturally independent existence may make him look upon what he owes to the common cause as a gratuitous contribution, the loss of which will do less harm to others than the payment of it is burdensome to himself; and, regarding the moral person which constitutes the State as a persona ficta, because not a man, he may wish to enjoy the rights of citizenship without being ready to fulfil the duties of a subject. The continuance of such an injustice could not but prove the undoing of the body politic. In order then that the social compact may not be an empty formula, it tacitly includes the undertaking, which alone can give force to the rest, that whoever refuses to obey the general will shall be compelled to do so by the whole body. This means nothing less than that he will be forced to be free; for this is the condition which, by giving each citizen to his country, secures him against all personal dependence. In this lies the key to the working of the political machine; this alone legitimizes civil undertakings, which, without it, would be absurd, tyrannical, and liable to the most frightful abuses.