Christians in this World

The Epistle of Mathetes to Diognetus was written in the late 2nd century by an unknown disciple, self-described as a "disciple of the apostles" to a Roman teacher who was likely the tutor to Marcus Aurelius. Though an ideal, it is a wonderful description of how Christians can approach their lives in this world - lives lived here but belonging to God.

For Christians are not distinguished from the
rest of mankind either in locality or in speech or in customs. For they dwell not somewhere in cities of their own, neither do they use some different language, nor practise an extraordinary kind of life. Nor again do they possess any invention discovered by any intelligence or study of ingenious men, nor are they masters of any human dogma as some are. But while they dwell in cities of Greeks and barbarians as the lot of each is cast, and follow the native customs in dress and food and the other
arrangements of life, yet the constitution of their
own citizenship, which they set forth, is marvellous,
and confessedly contradicts expectation. They dwell in their own countries, but only as
sojourners; they bear their share in all things as
citizens, and they endure all hardships as strangers.
Every foreign country is a fatherland to them, and
every fatherland is foreign. They marry like all other men and they beget
children; but they do not cast away their offspring. They have their meals in common, but not their
wives. They find themselves in the flesh, and yet they
live not after the flesh. Their existence is on earth, but their
citizenship is in heaven. They obey the established laws, and they
surpass the laws in their own lives. They love all men, and they are persecuted by
all. They are ignored, and yet they are condemned.
They are put to death, and yet they are endued with
life. They are in beggary, and yet they make many
rich. They are in want of all things, and yet they
abound in all things. They are dishonoured, and yet they are
glorified in their dishonour. They are evil spoken of,
and yet they are vindicated. They are reviled, and they bless; they are
insulted, and they respect. Doing good they are punished as evil-doers;
being punished they rejoice, as if they were thereby
quickened by life. War is waged against them as aliens by the
Jews, and persecution is carried on against them by
the Greeks, and yet those that hate them cannot tell
the reason of their hostility.