Irenaeus was the first of the early fathers to speak unequivocally of a "New" Testament parallel to the Old. But the idea that this was inspired Scripture was not an innovation. St. Peter writing in his second letter places Paul's letter on the level of the "other scriptures," that is, the Old Testament. By approximately the middle of the second century the church had roughly defined collection of Christian writings which were treated as scripture. Ironically, the first to draft a canon was Marcion the heretic. Marcion accepted the Old Testament as literally true; he did not agree with the allegorical methods of exegesis then en vogue in the Church. He found the the legalism and strict justice of the Old Testament impossible to reconcile with God's redeeming love and grace in the New Testament writings. He therefore concluded that there must be two "gods:" the god of Judaism, known as the Lower Demiurge, which created the universe, and the supreme God revealed in Christ. St. Paul who was openly outspoken against the law, was Marcion's hero. But Marcion's ideas smacked of the then-contemporary gnosticism. He also regarded any Judaizing passages with a jaundiced eye, so that when he compiled his canon of scripture, he removed all Judaizing passages in St. Luke's gospel. The Church was then compelled to create an agreed list of books for the canon. The earliest document which contains the twenty-seven books we recognize as New Testament Scripture today was St. Athanasius' paschal letter of 367 AD; the acceptance of this list became universal some 150 years later.
Christianity inherited from Judaism the concept of divinely-inspired scripture; many religions had sacred texts but only Judaism claimed its text to be divinely inspired by one supreme God. When Christ or the Apostles quoted the Old Testament, they clearly regarded the Old Testament as scripture. St. Paul affirms in 2 Timothy 3:16 that "all scripture is given by inspiration of God..." Obviously he is referring to the Old Testament here as the New Testament had not yet come into being. Christ freely took upon Himself the mantle of the Messiah, whose concepts He applied to Himself and to His mission. This set the precedent that the Old Testament could be read as a completely "Christian" text. The whole pattern of the Christian revelation was set forth by the Apostles as "according to the scriptures." Christ is to be understood as the fulfillment of the "law of Moses, and the prophets, and the Psalms." The ultimate warrant for this conviction was Christ's own example and authorization. According to Barnabas, the "fatal error" of the Jews was to allow themselves to be taken by the literal sense of scripture: what God really wanted was not blood sacrifices as the Mosaic law prescribed, but rather a contrite heart; not bodily fasting but good works; not abstention from certain foods, but rather from the vices associated with them, and so on. Origen views the Old Testament and New Testament as a symphony; one comes before and the other follows Christ's incarnation, and there is no difference or conflict between them. Augustine indicated that in the Old Testament the New is concealed and in the New Testament the Old is revealed - the New Testament draws out what is contained in the Old Testament.
The method of exegesis alluded to in the above paragraph has come to be known in modern times as "typology." The church fathers used various terms to describe this method. "Allegory" was suggested to them by St. Paul (Galatians 4:24) in his relating that Abraham's two sons were an "allegory" of the two covenants. But this caused confusion and today is best avoided. The word "typology" today connotes a somewhat different meaning than it did then, and therefore the distinction between its meaning then and now needs to be elucidated.
In allegorical exegesis the sacred text is treated as a mere symbol, or allegory, of spiritual truths. The literal and/or historical sense of the text plays a relatively minor role. The objective of the exegete is to bring out the theological, moral, or mystical meaning each verse (or even word) is thought to contain. A classic example of this sort of interpretation is Augustine's well-known explanation of the parable of the Good Samaritan: the traveler on the road stands for Adam, Jerusalem for the heavenly city from which he fell, Jericho for his resulting morality, the thieves for the devil and his angels, the priest and the Levite for the ineffective ministrations of the old covenant, the Samaritan for Christ, the inn for the church, and so forth. Philo made use of allegory to bridge the chasm between Old Testament revelation and his own platonizing philosophy. Philonic allegorism was able to detect, or infuse, a Christian significance into the least likely passages of the Old Testament. Gnostics were even bolder still, applying allegory to the life of Christ as symbolism mirroring the drama of the eons.
On the other hand typological exegesis worked along different paths. This method of exegesis brings out the corresponding difference between the two Testaments. It was based on the belief that the events and persons of the Old Testament were 'types' of, that is to say, prefigured and anticipated, the events and persons of the New Testament. Typology took history seriously, after all, it was the scene of the progressive unfolding of God's redemptive purpose. This means that from creation to the Judgment, the same unwavering plan could be seen in the sacred story. The earlier stages were shadows or rough sketches of what was to come, and Christ and His church were the climax. In all His dealings with mankind God was leading up to the Christian revelation, and the experiences of God's chosen people are pointers to this unveiling. Typology is the traditional Christian exegesis and its roots are firmly anchored in the Biblical view of history, in contrast to allegory. The value of typology as the method of scriptural interpretation was demonstrated as the Church struggled against the Marcionites who attempted to separate the two Testaments.
Two schools began to emerge in patristic exegesis, the Antiochene and Alexandrian schools. The former was characterized by its more literal, typological approach to scripture, the latter was characterized by its allegorical approach to scripture. This should not be taken too far however; the underlying unity of scriptural interpretation should not be overlooked. There was general agreement on types such as Adam and Moses foreshadowing Christ, the Flood pointing to baptism and the Judgment, the pre-eminent sacrifice of Isaac anticipating that of Calvary, the crossing of the Red Sea and the eating of manna looking forward to baptism and Eucharist, and so forth. The transition to an allegorical interpretative method of scriptural interpretation was tempting due to a Hellenistic culture infused with Platonic idealism, with its attractive theory of the whole of the visible order symbolizing invisible realities. It's not terribly surprising, then, that many of the fathers wrote a strain of allegory, some of them a very visible one, into their typology. In the second and third centuries Alexandria became known for its catechetical school and became the home of allegorical exegesis. Origen was Alexandria's great exponent of the allegorical method.
Origen was an admirer of Philo who regarded scripture as a vast ocean or forest of mysteries. It was impossible to fathom, or even perceive them all. One could be certain however that every jot and tittle was replete with meaning. Origen distinguished three levels of interpretation of scripture, corresponding to the body, the psychic, and the spiritual. The first was the straightforward historical sense. The second was the moral sense - the lesson of the text for the will. The third was the mystical sense with relation to Christ, the Church, or the great truths of the faith. If we apply this to the Psalmist's "Thou, O Lord art my support, my glory and the lifter up of my head," Origen would say that firstly, David speaks; secondly, it is Christ who knows His passion; thirdly, it is every just soul who by union with Christ finds his glory in God. Origen was able to extend his method to almost infinite interpretations. He believed that the allegorical method made it possible to interpret in a "manner worthy of the Holy Spirit." He would even borrow from the Gnostic technique and see in Christ's life an image of events in the spiritual realm. The theologians of Alexandria who followed Origen were all to one extent or another predisposed towards allegorical interpretation. This tradition was passed to the West, visible in the writings of Hilary and Ambrose. The great Latin exegete Jerome accepted Origen's senses of scripture, though in his later days he became suspicious of allegorism. Augustine employed allegory with abandon, delighting particularly in the mystical significance attached to names and numbers. Through the will of the Holy Spirit, Augustine believed, a passage could have multiple interpretations. Additionally Augustine listed four senses of scripture - the historical, the etiological, the allegorical and the figurative. More generally, love was paramount: Augustine thought no interpretation could be correct which did not promote the love of God or man.
And so allegorical exegesis became established in the Church. However, most of its later exponents were more circumspect and did not accept Origen's wilder ideas. Even so, a vigorous reaction against allegorical interpretation manifested itself in the fourth and fifth centuries. Centered in Antioch, the ecclesiastical metropolis Syria, the tradition of Bible study with meticulous attention to the text flourished. The main theologians of this tradition were Diodore of Tarsus (330-390), Theodore of Mopsuestia (350-428), and Theodoret (393-460). Practical illustrations of the Antiochian method are to be found in the sermons of St. John Chrysostom (347-407). The Antiochene school was unified in believing that allegorical methods were neither reliable nor legitimate instruments for scriptural interpretation. In the instances where deeper spiritual meanings were not fully explicit, the key was called "insight," (theoria) i.e. the power of perceiving, in addition to historical facts, the spiritual reality to which the facts were designed to point. Therefore they accepted a typology proper - a "prophecy expressed in terms of things." For theoria to operate properly, the Antiochenes considered the following necessary: (a) the literal sense of scripture should not be abolished; (b) there should be a real connection between spiritual discernment and historical fact; (c) these two objects be understood together, though clearly in different ways. As an example, Severan of Gabbala drew a parallel between the creatures which "the waters brought forth" and regeneration in baptism. Severan distinguished between forcing allegory out of history and preserving the history while discerning the theoria. Chrysostom brought out the same point when he divides scriptural statements into three categories: (a) those which allow a theoretic sense in addition to a literal sense; (b) those understood solely in the literal sense, and (c) those which only have a meaning other than the literal. Diodore in his turn does not forbid higher interpretation and theoria in his formula; however, he warns against letting theoria do away with the historical basis - theoria minus its historical basis is essentially allegory. Consistent with this Diodore freely admits Cain as prefiguring the synagogue, Abel the church and spotless lamb, Christ. Theodore similarly sees the sprinkling of blood on the doorposts at the Exodus as an authentic sign - or "type" - of our deliverance by Christ's blood. Diodore and Theodore's were very strict in applying the principles of anti-allegorical movement, which resulting in the elimination of practically all allegorical exegesis and severely limited the prophetic and typological elements. By contrast, Chrysostom and Theodoret adopted a more flexible approach; indeed, Chrysostom, while clearly preferring literal interpretation was known on occasion to employ the figurative sense as well.
Although allegorical interpretation is interesting and certainly within the tradition of the Orthodox Church, ultimately scriptural interpretation must admit the historicity of the events recorded in the Bible to have any basis in reality. While it is not necessary to say that King David ruled for exactly 40 years, or that God created the world in exactly 7 days, we acknowledge that there was a King David, and that God did create the world. The danger of extreme allegorism is that one can become so abstract in interpretation as to question the veracity of the Biblical account altogether. For example, once one asserts that a pericope might have been inserted by an editor after a book was written solely in order to communicate a spiritual or moral message, one can then question the truthfulness of any of the pericopes in that book. On the other hand the pitfalls of extreme historical-textualism is that one can miss very obvious "types" - for example, Abraham's sacrifice of Isaac prefiguring the sacrifice of Christ. Therefore it is best to maintain a balance between the two rich traditions of historicity (typology) and allegory.
J.N.D. Kelly, Early Christian Doctrines, HarperCollins Publishers, 1978