To choose the works of the first two centuries that can be called "classics" is a difficult, even an arbitrary, task. It is the purpose of this volume to select a number of the most notable treatises, having in mind their representative character as well as their intrinsic worth. Thus an early sermon has been included despite its somewhat banal nature, while more weighty works such as the Apologies of Tatian and Theophilus have been excluded. Justin and Athenagoras must suffice to indicate that class of literature. It has not, however, been possible to include every type of early Christian writing. There is no apocalypse, no apocryphal gospel, no Christian poetry. Yet the selection made will give a good indication of the temper of second century Christianity and the quality of its literature.
The earliest Christian writings after the New Testament are customarily known under the title "Apostolic Fathers." It is to a French scholar of the seventeenth century, Jean Cotelier, that we owe this grouping. In 1672 he published two volumes entitled SS. Patrum qui temporibus apostolicis floruerunt . . . opera edita et inedita, vera et suppositicia. This collection included the letter ascribed to Barnabas, the Shepherd of Hermas, two letters of Clement (of which only one is genuine), seven of Ignatius, and one of Polycarp, along with the account of the latter's martyrdom. All but Barnabas and Hermas will be found in this volume. Later on, the anonymous brief addressed to Diognetus and the fragments of Papias and Quadratus were added to the collection by Andreas Gallandi in his Bibliotheca veterum Patrum, 1765. Finally, with the discovery of the Didache by Byrennios in 1873, this tractate too came to find a place in editions of the Apostolic Fathers.
These writings do not form a unity either in date or in type. The earliest is Clement's Letter, about A.D.96. The latest are the sermon mistakenly known as his Second Letter, and the brief addressed to Diognetus. Both these were written somewhat before the middle of the second century. Other Christian literature not included in the Apostolic Fathers also comes from this period, as, for instance, the Apology of Aristides (about A.D.130) and the Odes of Solomon (before A.D.150). Yet, on the whole, the collection can be said to comprehend most of the significant Christian literature between the New Testament period and that of the great Apologists.
In type, the letter predominates. Even the account of Polycarp's martyrdom is a letter, from the church of Smyrna to that of Philomelium. The Letter of Barnabas is a theological tract, which attempts to grapple with the problem of the significance of the Old Testament for Christianity. It is a good example of the use of the epistolary form for a literary convention. Another instance is the piece addressed to Diognetus. While it bears the title of a letter, it is really a brief for Christianity. The earliest Christian sermon, as we have observed, is misleadingly called "Clement's Second Letter." Actually, however, it is a homily, and only by accident did it get dubbed an epistle.
Of the other works in this group, the Shepherd of Hermas is an apocalpyse, dealing with repentance after baptism; the Didache is a Church manual; while the fragments of Papias and Quadratus are from theological treatises. The former wrote five books entitled Explanations of the Lord's Sayings. They were apparently a running commentary on Jesus' utterances, interspersed with a good deal of oral tradition. Quadratus' work was an apology addressed to the emperor Hadrian.
What marks these writings, taken as a whole, is their literary simplicity, their earnest religious conviction, and their independence of Hellenistic philosophy and rhetoric. They are closer to the New Testament in their artlessness, and while they may lack something of its spiritual depth, they reveal an intense concern for its basic message. They come from a time when the Church was warring on two fronts -- against pagan attack and internal schism. Hence their peculiar concern is for order. The unity of the Church around its leaders and the preservation of the faith from perversion are their dominant themes. In consequence the religious spontaneity of the New Testament writings gives place to a more moral and ecclesiastical note.
The next important group of Christian writings in the second century is that of the Apologists. The earliest is perhaps the brief addressed to Diognetus. There follow the Apologies of Aristides, Justin, Tatian, Athenagoras, Theophilus, and, by the end of the century, of Clement of Alexandria and Tertullian. They are notable contributions to Christian literature. In Athenagoras, Clement, and Tertullian emerge writers of no small literary merit, who can vie with the best rhetoricians of the day. Their purpose is to defend the faith by making contact with the prevalent philosophies and by showing the superiority of Christianity. By means of the Logos doctrine which appears in John's Gospel and is clearly formulated in Justin, they relate the revelation in Christ to a current way of thinking. But their leading theme is monotheism; and their sharpest attacks fall on the weaknesses of the ancient mythology. They do not primarily emphasize the place of Jesus Christ in the faith. They are addressing Gentiles who are not inheritors of the Old Testament monotheism. Hence the unity of God is their first concern. Particularly is this true of Athenagoras' Plea.
A third group of early Christian writings is the apocryphal literature.  Of this a great deal has come down to us. Much of it, however, is later than the second century, and much of it is heretical in nature, being tinged with a Docetic point of view. In general this literature is Christian romance. There are tales of Jesus and the apostles which are told to satisfy the curiosity awakened by the paucity of incident in many of the New Testament accounts, and to meet the yearning for the miraculous. Popular folklore is blended with Gospel material, and legend upon legend is created in the style of a novelist with a pious imagination.
Then there is Christian poetry. Little of this has survived, the most significant work being the Odes of Solomon.  This is the first Christian hymnbook that we possess. It was almost certainly written in Greek sometime before A.D.150, though it has come down to us only in Syriac, and in a partial Coptic version. The Odes are hymns of praise, displaying a mystical spirit akin to that of John and Ignatius, and free from speculative thought.
Another group of early Christian writings is composed of the stories of martyrdoms. The simple but stirring tale of Polycarp's suffering forms the theme of the Letter of the Church of Smyrna to that of Philomelium. Other important accounts concern the persecutions in Lyons and Vienne; the martyrdoms of Perpetua and Felicitas in Carthage; of Carpus, Papylus, and Agathonice in Pergamon; and of Apollonius in Rome.  There have also been preserved some official court proceedings of the trials and executions of Christians. Notable are those of Justin, and of the martyrs of Scili in North Africa.
Finally, there are the Christian forms of Gnostic and anti-Gnostic literature. Most of the former has perished, though excerpts in the writings of Church Fathers enable us to reconstruct the systems of the great Gnostic teachers such as Valentinus, with some accuracy.  A number of the early Fathers wrote against Gnosticism -- Justin, Rhodo, Melito, Theophilus, Modestus, and others -- but their works have not survived. The five books of Irenaeus, Refutation and Overthrow of the Pretended but False Gnosis (usually referred to as Against Heresies), are the first full-length treatise we have giving the Catholic reply to various Gnostic systems. It is, indeed, more than this, for it includes a careful exposition of the faith; and it is unfortunate that its text has been preserved only in a Latin translation. The significance of Irenaeus cannot be over-estimated. While he is neither a penetrating nor a systematic thinker, he sums up the main lines of the Catholic development of the second century; and from him there flow the two differing streams of Western and Eastern Christianity.
Such are the types of Christian writing in the first two centuries. Almost all of it was penned by Gentiles. Practically no Jewish Christian literature has survived. It is possible that Clement of Rome and Hermas were Hellenistic Jews; and it is to our loss that the Memoirs of Hegesippus, a Hellenistic Jew of the Orient, have perished. These Memoirs comprised five books and constituted a polemic against Gnosticism. They contained also some historical details of the early Palestinian Church, of which Eusebius has preserved some fragments in his Ecclesiastical History. At the end of the second century one of the main sources underlying the pseudo-Clementine literature  was written; and this gives us some knowledge of Jewish Christianity. But it is remarkable with what rapidity the Christian faith, born in the obscure environment of Galilee, should have become a Gentile religion, enlisting the efforts of Gentile writers of distinction, while Jewish Christianity should have dwindled in importance. Judaizers were, to be sure, a force to be reckoned with in the days of Ignatius, and from time to time we hear of them in the writings of later Church Fathers such as Epiphanius. But they have left no significant body of literature. Separated from their countrymen by their religious convictions, and from the Holy City by the destruction under Titus, Jewish Christians eked out a precarious and isolated existence, until, having splintered into various groups, they were almost extinct by the fifth century, though a number of their ideas survived in Islam. It was the Greek, rather than the Jew, who became the inheritor of the Christian message-a fact which should give pause to those who unduly exaggerate the importance of Hebrew above Greek thinking.
 See the collection made by M. R. James, The Apocryphal New Testament. Oxford, 1924.  J. R. Harris and A. Mingana, The Odes of Solomon, 2 vols. Manchester, 1916-1920.  A selection has been translated and published by E. C. E. Owen, Some Authentic Acts of the Early Martyrs. 1927.  A notable document, for instance, is the letter of Ptolemy to Flora, preserved in Epiphanius' Panarion. See the new edition by G. Quispel, Éditions du Cerf, Paris, 1950 (in Sources chrétiennes). An English translation is given by R. M. Grant in his Second Century Christianity, pp. 30-37. S.P.C.K., London, 1946.  I.e., The Sermons of Peter. See the recent study by H. J. Schoeps, Theologie und Geschichte des Judenchristentums. J. C. B. Mohr, Tübingen, 1949.
 J. R. Harris and A. Mingana, The Odes of Solomon, 2 vols. Manchester, 1916-1920.
 A selection has been translated and published by E. C. E. Owen, Some Authentic Acts of the Early Martyrs. 1927.
 A notable document, for instance, is the letter of Ptolemy to Flora, preserved in Epiphanius' Panarion. See the new edition by G. Quispel, Éditions du Cerf, Paris, 1950 (in Sources chrétiennes). An English translation is given by R. M. Grant in his Second Century Christianity, pp. 30-37. S.P.C.K., London, 1946.
 I.e., The Sermons of Peter. See the recent study by H. J. Schoeps, Theologie und Geschichte des Judenchristentums. J. C. B. Mohr, Tübingen, 1949.