The origins of the Epistle to Diognetus are surrounded in mystery, though for reasons we will discuss there is strong evidence that it is amongst the earliest extra-biblical books. While this letter to “Diognetus” [common name in ancient Rome] is often ascribed to Mathetes [“disciple”], neither name gives us much of a clue about the identities of these men. However, internal evidence from the text itself tells us quite a bit.
The Letter’s Historical Context. As for the epistle’s date we can surmise an early date of composition. The text informs us that the Jews were still conducting sacrifices (Chapters 3-4), something that Clement relates was happening in his own day. Also like Clement, there appears to be a lack of written Gospels, as their content is paraphrased and obliquely referred to, but never quoted. Both of these clues point to a date close to that of Clement’s, which for reasons covered in the previous link, would probably be between the years 65 to 85 AD.
We also have more clues of a very early date: internal evidence suggests that the author was taught directly by Paul or one of his associates. The author says he knew the Apostles (Chapter 11) and he calls Paul “the Apostle” (Chapter 12). Further, throughout the work Paul’s ideas are often paraphrased or quoted in short snippets, perhaps indicating that he picked up these ideas not directly from reading Paul’s letters as he is obviously quoting from memory having fully synthesized his teaching.
While there are some scholars who posit that the last two chapters of the Epistle to Diognetus are later interpolations, and others that posit a date in the second century, the evidence for either of these contentions is ultimately unconvincing. For one, there was only one surviving manuscript of the letter, until it was destroyed by marauding Germans in 1870. So, we have no manuscript evidence of there ever have been interpolations made, as there was only one known manuscript in which we have been bequeathed the letter’s content. Those who posit interpolations are simply imagining them, for there is no direct evidence of it. Second, the work has none of the hallmarks of the second century Greek apologists. It does not belabor itself going over details of Greek philosophy nor does it address any second century developments in Christian history, such as Gnosticism. In summation, we have no internal evidence at all that the epistle was written in the second century.
We do have one piece of external evidence for a second century date: the letter was found in a 12th century codex of Justin Martyr’s writings. It is worth saying that there is no one today who thinks Justin Martyr wrote it, but probably for the wrong reasons. Many will say it bears no resemblance to his thought, but none of us knew Justin personally so ultimately we cannot prove what his thought would have sounded like in every situation. Our best evidence that it is not written by Justin is that Justin nowhere claims to have known the Apostles. In fact, we actually do know how he was converted and he fails to mention having intercourse with Apostles. Further, there is no evidence that there were still Jewish sacrifices going on in his day.
The chances of the letter being a forgery are also next to nothing. It has too many small details that appear too much like someone’s genuine thoughts to have been a forgery. Further, the letter takes on no controversies which would have required such a creative, subtle forgery. Being that the letter is essentially ascribed to Justin, but it contains historical details that would not permit us to believe such an ascription to be genuine, this gives us reason to believe that the only forgery is its ascription and the work itself is of an earlier, genuine nature. After all, if the letter was originally intended as a forgery, why not ascribe it to someone more important, fitting the historical details of the letter itself? A forger would dream up an author like Clement, Dionysus the Areopagite, Luke, or maybe even Apollos. The fact that this is not the case gives us good reason to believe the letter is not a forgery and its original author is someone who was unremarkable–hence the need later on to ascribe it to someone who was more notable, such as Justin Martyr.
So, how did the letter survive? The letter was never quoted in antiquity. It must have been considered somewhat unimportant. Ultimately, we have no idea why the letter, with an unremarkable author and no real popularity, has barely made it to us today. Perhaps, its content was considered so valuable and concise that like the Prayer of Manasseh it was kept as an appendix to other works of an early nature (apparently Justin’s) “lest it perish entirely.”
The Letter’s Teaching. What were the letter’s main teachings that, in light of its unremarkable author, makes it important to us today? In short, it preserves for us the Church’s earliest theory on the atonement (closest to the modern theory of Penal Substitution), speaks of the Biblical truth of man’s free will but God’s ability to grant to man an improved will to know Him and do His works, salvation by faith and not of works, and the necessity of good works as the fruit of faith. Many of these ideas, so important to modern Protestantism, were mentioned but hardly emphasized by the early Church. In the Epistle to Diognetus, they are not mere mentions in passing–they are the substance of the work.
Without further ado, the following are highlights from the letter–
God gives us wisdom to understand and preach His name:
I implore God, who enables us both to speak and to hear, to grant to me so to speak, that, above all, I may hear you have been edified, and to you so to hear, that I who speak may have no cause of regret for having done so (Chap 1).
God Himself…has sent from heaven, and placed among men, [Him who is] the truth, and the holy and incomprehensible Word, and has firmly established Him in their hearts…as a Saviour He sent Him, and as seeking to persuade, not to compel us; for violence has no place in the character of God (Chap 7).
At the time of writing, some Jews still performed sacrifices:
And next, I imagine that you are most desirous of hearing something on this point, that the Christians do not observe the same forms of divine worship as do the Jews…For while the Gentiles, by offering such things to those [idols] that are destitute of sense and hearing, furnish an example of madness; they, on the other hand by thinking to offer these things to God as if He needed them, might justly reckon it rather an act of folly than of divine worship (Chap 3).
Rejection of Jewish practices:
But as to their scrupulosity concerning meats, and their superstition as respects the Sabbaths, and their boasting about circumcision, and their fancies about fasting and the new moons, which are utterly ridiculous and unworthy of notice—I do not think that you require to learn anything from me (Chapter 4).
Christians are seen by their moral lives:
For the Christians are distinguished from other men neither by country, nor language, nor the customs which they observe…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 striking method of life. They dwell in their own countries, but simply as sojourners (Chapter 5).
God alone is good:
The crucifixion acts as a substitute for our lack of good works:
He approved the time of working iniquity which then was, but that He sought to form a mind conscious of righteousness, so that being convinced in that time of our unworthiness of attaining life through our own works, it should now, through the kindness of God, be vouchsafed to us…He Himself took on Him the burden of our iniquities, He gave His own Son as a ransom for us, the holy One for transgressors, the blameless One for the wicked, the righteous One for the unrighteous, the incorruptible One for the corruptible, the immortal One for those who are mortal. For what other thing was capable of covering our sins than His righteousness? By what other one was it possible that we, the wicked and ungodly, could bejustified, than by the only Son of God? O sweet exchange! O unsearchable operation! O benefits surpassing all expectation! That the wickedness of many should be hid in a single righteous One, and that the righteousness of One should justify many transgressors (Chap 9)!
Faith leads to good works:
If you also desire [to possess] this faith, you likewise shall receive first of all the knowledge of the Father…And when you have attained this knowledge, with what joy do you think you will be filled? Or, how will you love Him who has first so loved you? And if you love Him, you will be an imitator of His kindness (Chap 10).
For he who thinks he knows anything without true knowledge, and such as is witnessed to by life, knows nothing, but is deceived by the Serpent, as not loving life. But he who combines knowledge with fear, and seeks after life, plants in hope, looking for fruit. Let your heart be your wisdom; and let your life be true knowledge inwardly received (Chapter 12).
The author is an Apostolic Father and likely a disciple of Paul:
The Apostle [ο αποστολος], perceiving the force [of this conjunction], and blaming that knowledge which, without true doctrine, is admitted to influence life, declares,
Knowledge puffs up, but love edifies (Chap 12).