If the entire nation is one family, then there would seem to need to be a head of family. If the people of a country conceive of the ruler of that country as having received his/her authority directly from a god, then the authority of the institution of government of that country is supported by the authority of its institution of religion.
Divine rights of kings. The king as head of the nation as family can be claimed to rule because of having been chosen for that role by God.
The emperor of Japan is understood to be the direct descendant of the solar goddess Amaterasu.
The king, and later the emperor, of China was understand to have the conditional authority of God to rule the people as God's steward.