Some scholars date this wonderful work as early as 130 a.d., while others, mid to-late second century.
The Epistle of Mathetes to Diognetus
Chapter V - The Manners of the Christians
Christians are not distinguished from other men by country, language, nor by the customs which they observe. They do not inhabit cities of their own, use a particular way of speaking, nor lead a life marked out by any curiosity. The course of conduct they follow has not been devised by the speculation and deliberation of inquisitive men. The do not, like some, proclaim themselves the advocates of merely human doctrines.
Instead, they inhabit both Greek and barbarian cities, however things have fallen to each of them. And it is while following the customs of the natives in clothing, food, and the rest of ordinary life that they display to us their wonderful and admittedly striking way of life.They live in their own countries, but they do so as those who are just passing through. As citizens they participate in everything with others, yet they endure everything as if they were foreigners. Every foreign land is like their homeland to them, and every land of their birth is like a land of strangers.
They marry, like everyone else, and they have children, but they do not destroy their offspring. They share a common table, but not a common bed.
They exist in the flesh, but they do not live by the flesh. They pass their days on earth, but they are citizens of heaven. They obey the prescribed laws, all the while surpassing the laws by their lives.
They love all men and are persecuted by all. They are unknown and condemned. They are put to death and restored to life.
They are poor, yet make many rich. They lack everything, yet they overflow in everything. They are dishonored, and yet in their very dishonor they are glorified; they are spoken ill of and yet are justified; they are reviled but bless; they are insulted and repay the insult with honor; they do good, yet are punished as evildoers; when punished, they rejoice as if raised from the dead. They are assailed by the Jews as barbarians; they are persecuted by the Greeks; yet those who hate them are unable to give any reason for their hatred.