How is citizenship a critical aspect of Greek society and government?

Greek citizenship stemmed from the fusion of two elements, (a) the notion of the individual state as a 'thing' with boundaries, a history, and a power of decision, and (b) the notion of its inhabitants participating in its life as joint proprietors.

Explanation: .Ancient Greek and Roman societies granted their citizens rights and responsibilities that slaves, foreigners, and other people who were considered subordinate did not possess. Citizenship rights changed over time. While the Greeks tended to limit citizenship to children born to citizens, the Romans were more willing to extend citizenship to include others who had previously been excluded, such as freed slaves.

Citizenship in Ancient Greece. In Greece, citizenship meant sharing in the duties and privileges of membership in the polis, or city-state*. Citizens were required to fight in defense of the polis and expected to participate in the political life of the city by voting. In return, they were the only ones allowed to own land and to hold political office. Because citizens controlled the wealth and power of the polis, the Greeks carefully regulated who could obtain citizenship. In general, only those free residents who could trace their ancestry to a famous founder of the city were considered citizens. Only on rare occasions would a polis grant citizenship to outsiders, usually only to those who possessed great wealth or valuable skills.

* city-state independent state consisting of a city and its surrounding territory

unless they converted, many non-christians (mainly jews and muslims) were persecuted