The work now before us, The Demonstration of the Apostolic Preaching, has recently been found in an Armenian translation, and no portion of it seems to have survived in any other language.
This new treatise does not come upon us entirely as a surprise; for Eusebius  had mentioned its title, Eis epideixin tou apostolikou kerugmatos, and had said that it was addressed to "a brother named Marcianus." This is all he tells us; but we can now add from the book itself that it was written after the completion of the greater work, and therefore somewhere about A.D.180; and that Marcianus was on intimate terms with the writer, but absent from him at the time of writing.  The work Against Heresies is, of course, controversial from first to last: but the present treatise is a sort of Vade mecum for an intelligent Christian, explaining his faith, placing it in its historical setting in relation to Judaism, and confirming it by the citation and exposition of a great number of Old Testament passages. It is in no sense a manual for catechumens: it is a handbook of Christian Evidence, though its form is not controversial.
A tract of this kind from the pen of a great teacher in any age must needs be of interest. How was Christianity presented as a whole to an educated believer? What were the main points of doctrine and of life on which stress was laid? What were the grounds of belief. which appeared to be most convincing then? These are the things which the historian of religious development wants to know in each of the Christian centuries, and which he finds it exceptionally difficult to get at. The great events and the leading personalities have left their mark on the records of the time: the development of doctrine and the growth of ecclesiastical institutions can be traced with increasing clearness as the documents are tested and studied and compared: but the religious sense of an age, the beliefs which affected life, and the grounds of those beliefs, the ruling motives of conduct, the things that to the best minds seemed to matter most -- these escape us unless we are insistent in our search for them; and often, search as we will, we find little to reward our pains. We have special reason to be grateful for a plain statement of the Christian religion as it presented itself to a master mind at the end of the second century. A long and varied experience had qualified Irenæus for such a task. As a boy he had listened to St Polycarp at Smyrna, and he may have conversed with others -- the Elders, as he calls "Gnosticism," in all its divergent forms, with the Christian truth as he had come to conceive it in a long life of patient study and practical ministry. He had given to the Church his five books of The Exposure and Overthrow of Knowledge (Gnosis) falsely so called. When such a man lays controversy aside and takes up his pen to talk, as he says, to his absent friend, and furnish him with a summary statement of the Apostolic message and the reasons for believing it in terms of his own day, he deserves our close attention. We shall make little of him if we insist on judging him by modern standards: we shall miss the definiteness of post-Nicene doctrine; we shall be disappointed at finding nothing about ecclesiastical organization; we shall be distressed at the quaint conceits of his exposition of Old Testament prophecies. But if we come to him fresh from the study of Justin Martyr's First Apology, written some thirty-five years before, we shall appreciate the atmosphere in which he had grown up and shall recognize the advance which he had made in the thoughtful interpretation of the Faith.
The manuscript which contains our treatise was found in December 1904, in the Church of the Blessed Virgin at Eriwan in Armenia, by Dr Karapet Ter-Mekerttshian, one of the most learned of the Armenian clergy. It was edited by him with a translation into German, in conjunction with Dr Erwand Ter-Minassiantz, in 1907, in the Texte and Untersuchungen (xxxi.1); and Dr Harnack added a brief dissertation and some notes. Then in 1912 Dr Simon Weber, of the Faculty of Catholic Theology in the University of Freiburg in Breisgau, being dissatisfied with this presentation of the work, published a fresh translation with the help of some Armenian scholars. Neither of these translations satisfies the needs of English patristic students. The second, though it corrects some errors of the first, is far less close to the original text. And both are vitiated by a want of acquaintance with the textual criticism of the Septuagint and the Greek New Testament, and also with the larger work of St Irenæus himself. The present translation is an attempt to remedy these defects, and at the same time to bring the treatise to the knowledge of those who have hitherto been debarred by linguistic difficulties from reading it. My own acquaintance with the Armenian language and literature is so limited that I cannot hope to have altogether avoided mistakes, and I shall be grateful to those who will point them out. I owe very much to the first of the translations into German, and something also to the second: if I am sometimes right where they were wrong, it is mainly because I have sought to read the text in the light of what Irenæus has said elsewhere.
The same manuscript contains an Armenian version of Books IV and V of the great work Against Heresies.  These come immediately before our treatise, and are embraced with them under the single title, The Demonstration of the Apostolic Preaching. We cannot say whether this error of title goes back beyond the date of the manuscript, which was probably written between 1270-1289, that is in the time of the learned Archbishop John, the brother of King Hetum of Cilicia. A note at the end states that it was written for this archbishop. The Armenian editors believe that the same translator is responsible for the two books of the larger work and for our treatise, and that the translation was made at some date between 650 and 750.
The version of Books IV and V is of high value, as enabling us to check the Latin version, the MSS. of which differ considerably among themselves. It is useful also as illustrating the fondness of the Armenian translator for a double rendering of a single word of the original. When we read the Armenian and the Latin side by side, we gain the impression that the Greek text has been very closely followed; and thus we are assured that for our present treatise also the Armenian version is a faithful representative of the lost original.
 The Armenian translation of Bks. IV and V, found in the same MS. with our treatise, is a valuable aid for the criticism of these books.  Eccl. Hist., v. 26.  See chapters 1 and 99.  Published with a translation by the same editors in Texte u. Untersuchungen, xxxv. 2
 Eccl. Hist., v. 26.
 See chapters 1 and 99.
 Published with a translation by the same editors in Texte u. Untersuchungen, xxxv. 2