The Letter to Diognetus dates to sometime in the 2nd Century (approx. 130-180 AD), and is one of the earliest examples of Christian apologetics outside of the Bible. Apologetics is the practice of giving a defense of, or an explanation of, one’s faith for those who have questions or doubts.
The letter, whose author and recipient are unknown, gives us a glimpse into life and thought of early Christians as well as the way that people in their communities viewed them and thought of them.
Here is an excerpt from Chapter 5, on the topic of what sets Christians apart from others in society:
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.
This poetic and beautiful description of Christian lifestyle encourages me and challenges me to want myself, my family and my church to be seen as a counter-cultural community with convictions, who are for the community where we live because God so loved the world and He has poured his love into our hearts by the Holy Spirit.
The rest of the letter is also worth reading, particularly Chapters 6 & 9, the latter of which talks about the doctrine of justification.
You can read the letter in its entirety here.