Full Idea
By the original contract all members of the people give up their external freedom in order to receive it back at once as members of a commonweath.
Gist of Idea
In the contract people lose their rights, but immediately regain them, in the new commonwealth
Source
Immanuel Kant (Metaphysics of Morals I: Doctrine of Right [1797], §47)
Book Reference
Kant,Immanuel: 'Political Writings', ed/tr. Reiss,Hans [CUP 1996], p.140
A Reaction
This tries to give the impression that absolutely nothing is lost in the original alienation of rights. It is probably better to say that you give up one set of freedoms, which are replaced by a different (and presumably superior) set.