In the political system of pre-Revolutionary France, the nobility made up the Second Estate of the Estates General (with the Catholic clergy comprising the First Estate and the bourgeoisie and peasants in the Third Estate). Although membership in the noble class was mainly inherited, it was not a fully closed order.
The purpose of dividing the government into 3 different branches was that so one entity did not have all the power. So they basically did it to divide the power.
