All the letters found in the New Testament, the letter to the Hebrews and the letters of the apostles Peter and Paul, are addressed to Christians. As far as I know, the letter to Diognetus is the only known letter from early Christianity that is addressed to a non-Christian inquirer. The letter has been assigned the date A.D. 130. No one knows just who the writer was, nor the recipient either for that matter. However, the writer does identify himself as “a disciple of the apostles.” How wonderful that this letter is still available to read in our day! The letter has been divided into chapters, and the quote below is Chapter 5 in its entirety.
Christians are distinguished from other people neither by country, nor language, nor the customs which they observe. For they neither inhabit cities of their own, nor employ a language of their own, nor lead a life which is marked out by any singularity. The course of conduct which they follow has not been devised by any speculation or deliberation of inquisitive men; nor do they, like some, proclaim themselves the advocates of any merely human teachings. But, inhabiting Greek as well as barbarian cities, according as the lot of each of them has determined, and following the customs of the natives in respect to clothing, food, and the rest of their ordinary conduct, they display to us their wonderful and confessedly paradoxical way of life. They dwell in their own countries, but simply as sojourners. As citizens, they share in all things with others, and yet endure all things as if foreigners. Every foreign land is to them as their native country, and every land of their birth as a land of strangers. They marry, as do all others; they beget children; but they do not destroy their offspring [literally “cast away fetuses”]. They have a common table, but not a common bed. They are in the flesh, but they do not live after the flesh. They pass their days on earth, but they are citizens of heaven. They obey the prescribed laws, and at the same time surpass the laws by their lives. They love all people, 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 are in lack of all things, and yet abound in all; they are dishonoured, and yet in their very dishonour are glorified. They are evil spoken of, and yet are justified; they are reviled, and bless; they are insulted, and repay the insult with honour; they do good, yet are punished as evil-doers. When punished, they rejoice as if made alive; they are assailed by the Jews as foreigners, and are persecuted by the Greeks; yet those who hate them are unable to assign any reason for their hatred.