Translated by Alexander Roberts and James Donaldson.
The following interesting and eloquent Epistle is anonymous, and we have no clue whatever as to its author. For a considerable period after its publication in 1592, it was generally ascribed to Justin Martyr. In recent times Otto has inserted it among the works of that writer, but Semisch and others contend that it cannot possibly be his. In dealing with this question, we depend entirely upon the internal evidence, no statement as to the authorship of the Epistle having descended to us from antiquity. And it can scarcely be denied that the whole tone of the Epistle, as well as special passages which it contains, points to some other writer than Justin. Accordingly, critics are now for the most part agreed that it is not his, and that it must be ascribed to one who lived at a still earlier date in the history of the Church. Several internal arguments have been brought forward in favour of this opinion. Supposing chap. xi. to be genuine, it has been supported by the fact that the writer there styles himself "a disciple of the apostles." But there is great suspicion that the two concluding chapters are spurious; and even though admitted to be genuine, the expression quoted evidently admits of a different explanation from that which implies the writer's personal acquaintance with the apostles: it might, indeed, be adopted by one even at the present day. More weight is to be attached to those passages in which the writer speaks of Christianity as still being a new thing in the world. Expressions to this effect occur in several places (chap. i., ii., ix.), and seem to imply that the author lived very little, if at all, after the apostolic age. There is certainly nothing in the Epistle which is inconsistent with this opinion; and we may therefore believe, that in this beautiful composition we possess a genuine production of some apostolic man who lived not later than the beginning of the second century.
The names of Clement of Rome and of Apollos have both been suggested as those of the probable author. Such opinions, however, are pure fancies, which it is perhaps impossible to refute, but which rest on nothing more than conjecture. Nor can a single word be said as to the person named Diognetus, to whom the letter is addressed. We must be content to leave both points in hopeless obscurity, and simply accept the Epistle as written by an earnest and intelligent Christian to a sincere inquirer among the Gentiles, towards the close of the apostolic age.
It is much to be regretted that the text is often so very doubtful. Only three mss. of the Epistle, all probably exhibiting the same original text, are known to exist; and in not a few passages the readings are, in consequence, very defective and obscure. But notwithstanding this drawback, and the difficulty of representing the full force and elegance of the original, this Epistle, as now presented to the English reader, can hardly fail to excite both his deepest interest and admiration.
Reference address : https://www.ellopos.net/elpenor/greek-texts/fathers/diognetus/epistle-diognetus.asp?pg=2