Rousseau says, "property is the most sacred of all the rights of citizenship": What do you think he means by this, and why might property be the most important right of a citizen?

For readers in contemporary developed countries, where property rights are taken for granted, this saying can appear puzzling. It is important to read it in historical context, against the background of feudalism. The idea of property rights was enshrined for the English in the Magna Carta, signed by King John of England in 1215, along with the idea that even the king was not above the law and that everyone had the right to a fair trial. The French, under the power of an absolute monarch, lacked such rights.
Under the feudal system, all people were vassals of the king, holding land and property in return for service to the king. This meant, in theory, that the king could, at will, strip an individual of all property and rights. That meant that no one was truly free to criticize the king or oppose his policies until private property rights became established.
Property gives people freedom of action. In other words, someone who owns a home, and has an adequate income for necessities such as food, clothing, and medical care, is in a position to criticize injustice and speak freely. Someone who is dependent on the government or can be deprived of their property by a vindictive or authoritarian ruler simply for expressing an unpopular opinion, has no real freedom.
Also, as Marx later stated, freedom is freedom from economic necessity. In other words, a serf, who owned almost nothing and simply worked the land for a noble, on terms dictated by the noble, had no freedom to make any life choices. As one accumulates property (whether in the form of real property such as land or money), one is able to choose where to live, what employment to seek, whether to marry or remain single, and many other things, but without inalienable property, one lacks freedom of choice.