Christians are distinguished from other men neither by country, nor language, nor the customs which they observe. For they neither inhabit cities of their own, nor employ a peculiar form of speech, nor lead a life which is marked out by any singularity … But inhabiting Greek as well as barbarian cities, according as the lot of each of them has determined, and following the customs of the inhabitants in respect to clothing, food, and the rest of their ordinary conduct, they display to us their wonderful and confessedly striking method of life. They dwell in their own countries only as sojourners … They pass their days on earth, but they are citizens of heaven. They obey the prescribed laws by their lives. They love all men, and are persecuted by all.
Letter to Diognetus (c. 125-200), David W. Bercot, Ed., A Dictionary of Early Christian Beliefs, p. 133