After the initial problems regarding the continuity and authority of the hierarchy, the greatest guarantee of true continuity and authenticity was found in the Scriptures. Christians inherited (without debate at first) the Hebrew Bible as the Word of God to the people of God at a now superseded stage of their pilgrimage through history. If St. Paul’s Gentile mission was valid, then theMosaic Law was viewed as no longer God’s final word to his people. Thus, the Hebrew Bible began to be called the “old” covenant. There was some hesitation in the church about the exact books included. The Greek version of the Old Testament (Septuagint) included books (such as the Wisdom of Solomon, Ecclesiasticus, and others) that were not accepted in the Hebrew canon. Most, but not all, Gentile Christian communities accepted the Septuagintal canon. The 3rd-century Alexandrian theologian Origen and especially the Latin biblical scholar St. Jerome (4th–5th century) believed it imprudent to base theological affirmations on books enjoying less than universal recognition. The fact that in many English Bibles the parts of the Old Testament accepted in the Septuagint but not in the Hebrew canon are often printed separately under the (misleading) title Apocrypha is a tribute to these ancient hesitations.

The growth of the New Testament is more complex and controversial. The earliest Christians used oral tradition to pass on the story of Jesus’ acts and words, often told in the context of preaching and teaching. As the first generation passed away, however, the need for a more permanent and lasting tradition of the life of Jesus became apparent. St. Mark first conceived the plan of composing a connected narrative, probably in the decade before—or at some time near—70 ce, when the Temple was destroyed by the Romans. The Gospels that traditionally were thought to have been written by St. Matthew and St. Luke borrowed from Mark and were compiled in the generation after his Gospel. Toward the end of the 1st century and reflecting the persecutions of the emperor Domitian, the Gospel According to John was written. Nevertheless, even after the Gospels were in common circulation, oral tradition was still current; it may even have been preferred. The Gospels themselves, which were probably intended for pastoral uses, did not immediately assume the status of Scripture. Well into the 3rd century, new gospels were being compiled, such as the Gospel of Thomas and the Gospel of Judas, which were not incorporated into the canonical New Testament. The Synoptic Gospels seem to have been used by the apologist St. Justin Martyr at Rome about 150 ce in the form of an early harmony (or synthesis of the Gospels); to this, Justin’s Syrian pupil Tatian added the Gospel According to John to make his Diatessaron (according to the four), a harmony of all four Gospels so successful that in Mesopotamia (Tatian’s homeland) it virtually ousted the separate Gospels for 250 years. In the late 2nd century, St. Irenaeus accepted as the standard version of the Christian Scriptures the four Gospels and several other texts that would become part of the canonical New Testament.

On a second level of authority stood the apostolic letters, especially those of St. Paul. The first of the letters appeared about 50 ce, and well before 90 ce the main body of his correspondence was circulating as a corpus (body of writings). Paul’s letters were the earliest texts of the Christian Scriptures. In addition to them, there are the seven so-called Catholic Letters (i.e., James; I and II Peter; I, II, and III John; and Jude), which were among the last of the literature to be accepted as part of the canonical New Testament.

St. Paul’s antitheses of law and grace, justice and goodness, and the letter and the spirit were extended further than Paul intended by the radical semi-gnostic Marcion of Pontus (c. 140–150), who taught that the Old Testament came from the inferior vengeful Jewish God of justice and that the New Testament told of the kindly universal Father. As the current texts of Gospels and letters presupposed some divine revelation through the Old Testament, Marcion concluded that they had been corrupted and interpolated by Judaizers. Marcion therefore established a fixed canon of an edited version of Luke’s Gospel and some of the Pauline Letters (expurgated), and with Old Testament at all. He was ultimately denounced as a heretic.

The orthodox reaction (by such theologians as Justin, Irenaeus, and Tertullian in the 2nd century) was to insist on the Gospel as the fulfillment of prophecy and on creation as the ground of redemption. Reasons were found for accepting the four already current Gospels, the full corpus of Pauline Letters, the Acts of the Apostles, John’s Revelation (Apocalypse), and the Catholic Letters. On the authorship of the Letter to the Hebrews there were doubts: Rome rejected it as non-Pauline, and Alexandria accepted it as Pauline. The list once established was a criterion (the meaning of “canon”) for the authentic Gospel of the new covenant and soon (by transference from the old) became entitled the New Testament. (The Greek word diathēkē means both “covenant” and “testament.”) The formation of the canon meant that special revelation ended with the death of the Apostles and that no authority could be attached to the apocryphal gospels, acts, and apocalypses proliferating in the 2nd century.

The problem of theological authority

Third, a check was found in the creed, an authoritative profession of the faith. At baptism, after renouncing “the devil and his pomps,” initiates declared their faith in response to three questions of the form:

Do you believe in God the Father almighty? Do you believe in Jesus Christ his Son our Lord…? Do you believe in the Holy Spirit in the church and in the Resurrection?

In time, these interrogations became the basis of declaratory creeds, adapted for use by clergy who felt themselves required to reassure colleagues who were not especially confident of their orthodoxy. The so-called Apostles’ Creed, a direct descendant of the baptismal interrogation used at Rome by 200 ce, is similar to the creed used in Rome in the 3rd and 4th centuries. Each church (or region) might have its own variant form, but all had the threefold structure.

The internal coherence given by creed, canon, and hierarchy was necessary both in the defense of orthodox Christianity against gnostic theosophical speculations and also in confronting pagan society. The strong coherence of the scattered congregations was remarkable to pagan observers.