The Epistle to Diognetus has been called "the noblest of early Christian writings" by J. B. Lightfoot. Johannes Quasten said it "deserves to rank among the most brilliant and beautiful works of Christian Greek literature. The writer is a master of rhetoric, his sentence structure is full of charm....The content reveals a man of fervent faith and wide knowledge, a mind thoroughly imbued with the principles of Christianity" (Patrology, I, 251-52). Philip Schaff calls it that "short but precious document" and says the unknown author "must be ranked with the `great unknown' authors of Job and the Epistle to the Hebrews, who are known only to God" (History of the Christian Church, II, 699-700).
It is included among the works commonly known as the apostolic fathers, but it is different from the rest of those writings. The apostolic fathers were written to Christians, but the Epistle to Diognetus was written to and for outsiders. It is an apology, that is, a defense of the Christian faith, and it belongs among the Christian apologists more than among the apostolic fathers.
The Epistle to Diognetus was written to a high-ranking pagan, Diognetus. Several theories have been advanced as to who the author of the epistle was and who Diognetus was, but nothing is certain on either question. The date of the Epistle to Diognetus is probably in the mid-to-late second or very early third century. The only known manuscript of this work was lost in 1870 during the Franco-Prussian War when the library of Strasbourg burned.
The purpose of this article is to survey what the Epistle to Diognetus says about Christian ethics and the Christian life. The Christian life is a "way of life" (epitedeuma, BAGD, 302) which has come into the world from God (1.1). It is distinct from paganism and Judaism.
The author of the Epistle to Diognetus restates the traditional arguments against idolatry, reminding Diognetus that idols are made by the hands of man and are not real gods (2.1-10). An idol worshipper, rather than being elevated, becomes no better than the idols (2.5).
Next the author distinguishes Christianity from Judaism, especially a ritualistic, legalistic type of Judaism (3.1-4.6). Externals such as keeping the Sabbath, circumcision, or fastidiousness over ceremonies are not examples of "godliness" (4.5; theosebeia, "reverence for God, piety, religion," BAGD, 358; cf. 1.1; 6.4). What the author does not admit is that a pure ethic, such as in found in the prophets of the Old Testament, is quite compatible with a Christian ethic.
What distinguishes the Christian way of life is not something external, but something spiritual. The explanation in the Epistle of Diognetus of the uniqueness of the Christian life is so beautiful that it deserves to be quoted at length:
"Christians are not distinguished from the rest of humanity by country, language, or custom. For nowhere do they live in cities of their own, nor do they speak some unusual dialect, nor do they practice an eccentric lifestyle....While they live in both Greek and barbarian cities, as each one's lot was cast, and follow the local customs in dress and food and other aspects of life, at the same time they demonstrate the remarkable and admittedly unusual character of their own citizenship.
"They live in their own countries, but only as aliens; they participate in everything as citizens, and endure everything as foreigners. Every foreign country is their fatherland, and every fatherland is foreign. They marry like everyone else, and have children, but they do not expose their offspring. They share their food but not their wives. They are `in the flesh,' but do not live `according to the flesh.' They live on earth, but their citizenship is in heaven. They obey the established laws; indeed in their private lives they transcend the laws.
"They love everyone, and by everyone they are persecuted. They are unknown, yet they are condemned; they are put to death, yet they are brought to life. They are poor, yet they make many rich; they are in need of everything, yet they abound in everything. They are dishonored, yet they are glorified in their dishonor; they are slandered, yet they are vindicated. They are cursed, yet they bless; they are insulted, yet they offer respect. When they do good, they are punished as evildoers; when they are punished, they rejoice as though brought to life....Those who hate them are unable to give a reason for their hostility" (5.1-17).
The Epistle to Diognetus then compares the relationship of the church to the world with that of the soul to the body.
"In a word, what the soul is to the body, Christians are to the world. The soul is dispersed through all the members of the body, and Christians throughout the cities of the world. The soul dwells in the body, but is not of the body; likewise Christians dwell in the world, but are not of the world. The soul, which is invisible, is confined in the body, which is visible, in the same way, Christians are recognized as being in the world, and yet their religion remains invisible.
"The flesh hates the soul and wages war against it, even though it has suffered no wrong, because it is hindered from indulging in its pleasures, so also the world hates the Christians, even though it has suffered no wrong, because they set themselves against its pleasures. The soul loves the flesh that hates it, and its members, and Christians love those who hate them.
"The soul is enclosed in the body, but it holds the body together; and though Christians are detained, in the world as if in a prison, they in fact hold the world together. The soul, which is immortal, lives in a mortal dwelling; similarly Christians live as strangers amidst perishable things, while waiting for the imperishable in heaven....Such is the important position to which God has appointed them" (6.1-9).
This marvelous religion is the "truth" and comes from the "omnipotent Creator of all, the invisible God himself" as he has revealed himself to man, especially through his Son Jesus Christ (7.1-8.11; 11.1-8). When people lead "undisciplined" lives ruled by "pleasures and lusts," God, in his patience, uses these to show to us "our inability to enter the kingdom of God on our own" and "the powerlessness of our nature to obtain life" (9.1, 5). Then God's goodness makes us worthy through the atonement of Christ: "A ransom for us, the holy one for the lawless, the guiltless for the guilty, `the just for the unjust,' the incorruptible for the corruptible, the immortal for the mortal. For what else but his righteousness could have covered our sins?" (9.2-3).
According to the Epistle to Diognetus, then, the Christian life is a life of love and faith which is lived in response to the saving grace of God (9.5-10.3). "By loving him you will be an imitator of his goodness" (10.4). Only a few specifics are mentioned which give definition to the Christian life. Christians have a heartfelt love for one another (1.1). They love their neighbor and help those in need (5.11; 10.5-6). They even love their enemies (6.6). They are concerned with heavenly life, and they disregard the world and its pleasures (1.1; 6.5; 10.7). They are pure in regard to sexual relations (5.7). They do not live "according to the flesh" (5.8). They are obedient citizens (5.10). They do not fear physical death, but do fear the real death of eternal fire (10.7).
The Epistle to Diognetus presents a balanced approach to a Christian ethic. The pattern of what we should be comes from God. Goodness is defined by God's very nature, and we should be imitators of God. Due to Christ and his atonement we are enabled to become worthy before God. Our service to God is rendered, not through worshipping idols of wood or stone or through an empty ceremonialism, but by loving God, our neighbor, and even our enemies. Finally, to use an often repeated phrase, the church is in the world but not of the world.