Translated by Alexander Roberts and James Donaldson.
Introductory Note to the Epistle of Mathetes to Diognetus
[a.d. 130.] The anonymous author of this Epistle gives himself the title (Mathetes) "a disciple  of the Apostles," and I venture to adopt it as his name. It is about all we know of him, and it serves a useful end. I place his letter here, as a sequel to the Clementine Epistle, for several reasons, which I think scholars will approve: (1) It is full of the Pauline spirit, and exhales the same pure and primitive fragrance which is characteristic of Clement. (2) No theory as to its date very much conflicts with that which I adopt, and it is sustained by good authorities. (3) But, as a specimen of the persuasives against Gentilism which early Christians employed in their intercourse with friends who adhered to heathenism, it admirably illustrates the temper prescribed by St. Paul (2 Tim. ii. 24), and not less the peculiar social relations of converts to the Gospel with the more amiable and candid of their personal friends at this early period.
Mathetes was possibly a catechumen of St. Paul or of one of the apostle's associates. I assume that his correspondent was the tutor of M. Aurelius. Placed just here, it fills a lacuna in the series, and takes the place of the pseudo (second) Epistle of Clement, which is now relegated to its proper place with the works falsely ascribed to St. Clement.
Altogether, the Epistle is a gem of purest ray; and, while suggesting some difficulties as to interpretation and exposition, it is practically clear as to argument and intent. Mathetes is, perhaps, the first of the apologists.
The following is the original Introductory Notice of the learned editors and translators: —
 apostolon genomenos mathetes. Cap. xi.
Reference address : https://www.ellopos.net/elpenor/greek-texts/fathers/diognetus/epistle-diognetus.asp