I've been familiar with this remarkable text for a while, but it was good to be reminded of it today. It presents and image of what Christians can be, and are called to be, and a reminder of why the early Church spread the faith of Jesus so widely in spite of persecution and disdain. Here's a selection from the section known as 'the Church in the world.'
For Christians cannot be distinguished from the rest of the human race by country or language or customs. They do not live in cities of their own; they do not use a peculiar form of speech; they do not follow an eccentric manner of life. This doctrine of theirs has not been discovered by the ingenuity or deep thought of inquisitive people, nor do they put forward a merely human teaching, as some people do. Yet, although they live in Greek and barbarian cities alike, as each one's lot has been cast, and follow the customs of the country in clothing and food and other matters of daily living, at the same time they give proof of the remarkable and admittedly extraordinary constitution of their own commonwealth. They live in their own countries, but only as aliens. They have a share in everything as citizens, and endure everything as foreigners. Every foreign land is their homeland, and yet for them every homeland is a foreign land. They marry, like everyone else, and they beget children, but they do not cast out their offspring. They share their board with each other, but not their marriage bed. It is true that they are "in the flesh," but they do not live "according to the flesh." They busy themselves on earth, but their citizenship is in heaven. They obey the established laws, but in their own lives they go far beyond what the laws require. They love all people, and by all people are persecuted. They are unknown, and still they are condemned; they are put to death, and yet they are brought to life. They are poor, and yet they make many rich; they are completely destitute, and yet they enjoy complete abundance. They are dishonoured, and in their very dishonour are glorified; they are defamed, and are vindicated. They are reviled, and yet they bless; when they are affronted, they still pay due respect. When they do good, they are punished as evildoers; undergoing punishment, they rejoice because they are brought to life. They are treated by the Jews as foreigners and enemies, and are hunted down by the Greeks; and all the time those who hate them find it impossible to justify their enmity.
To put it simply: What the soul is in the body, that Christians are in the world.