For Christians are not distinguished from the rest of humanity by country, language, or custom.
For nowhere do they live in cities of their own, nor do they speak some unusual dialect, nor do they practice an eccentric way of life.
This teaching of theirs has not been discovered by the thought and reflection of ingenious people, nor do they promote any human doctrine, as some do.
But while they live in both Greek and barbarian cities, as each one’s lot was cast, and follow the local customs in dress and food and other aspects of life, at the same time they demonstrate the remarkable and admittedly unusual character of their own citizenship.
They live in their own countries, but only as nonresidents; they participate in everything as citizens, and endure everything as foreigners.
Every foreign country is their fatherland, and every fatherland is foreign.
They marry like everyone else, and have children, but they do not expose their offspring [to kill them].
They share their food but not their wives.
They are in the flesh, but they do not live according to the flesh.
They live on earth, but their citizenship is in heaven.
They obey the established laws; indeed in their private lives they transcend the laws.
They love everyone, and by everyone they are persecuted.
They are unknown, yet they are condemned; they are put to death, yet they are brought to life.
They are poor, yet they make many rich; they are in need of everything, yet they abound in everything.
They are dishonored, yet they are glorified in their dishonor; they are slandered, yet they are vindicated.
They are cursed, yet they bless; they are insulted, yet they offer respect.
When they do good, they are punished as evildoers; when they are punished, they rejoice as though brought to life.
By the Jews they are assaulted as foreigners, and by the Greeks they are persecuted, yet those who hate them are unable to give a reason for their hostility.
(From The Epistle to Diognetus, Chapter 5, written perhaps between 117 and 225 AD posted on http://thegospelcoalition.org/blogs/justintaylor/2012/11/27/christianity-where-every-foreign-country-is-fatherland-and-every-fatherland-is-foreign/ )