How the Biblical Canon Was Formed
κανών — kanon · kah-NOHN
In brief
The "canon" is the list of books the Church receives as Holy Scripture — the rule by which she measures her preaching. The Church did not invent these books or vote them into existence; she recognized, over generations, the writings in which the apostolic faith was truly heard. The Old Testament came to her through the Greek Septuagint; the New Testament canon settled gradually, reaching its familiar twenty-seven-book shape by the fourth century. Throughout, the Bible is received within the Church, never above it.
Recognized, not invented
A common picture has a committee of bishops at some late council choosing which books would be "the Bible" and suppressing the rest. That is not what happened. The Church did not invent her Scriptures; she recognized them — the way an ear recognizes a familiar voice. Long before any formal list existed, the Gospels and the letters of Paul were already being read at the Sunday gathering, copied, and carried from church to church. The councils that eventually named the books were confirming a usage that had grown up over generations, not conjuring one into being.
The word canon is itself a clue. It is Greek for a measuring rod or rule — the standard against which other things are checked. To call a book "canonical" is not to grant it authority but to acknowledge the authority it already carries: the Church measures her preaching by these books because these are the books in which the apostolic faith is heard.
The Old Testament the apostles used
The Church was born with a Bible already in hand — the Scriptures of Israel, read in most of the first Christian congregations in their Greek form, the Septuagint. When the apostles "reasoned with them out of the scriptures" that Jesus is the Christ (Acts 17:2-3), these were the writings they opened. The Septuagint carried a somewhat wider collection than the Hebrew canon the rabbis later fixed, and the Church kept the wider collection: the books she calls the Anagignoskomena remain in the Orthodox Old Testament to this day. There was never a single dramatic decision about the Old Testament; the Church went on reading the Bible she had received.
How the New Testament came into focus
The New Testament settled more gradually, and the gradualness is worth seeing clearly. The four Gospels and the major letters of Paul were accepted almost everywhere very early; a handful of shorter books — Hebrews, James, 2 Peter, 2 and 3 John, Jude, Revelation — were received in some regions before others, and a few edifying early writings, such as the Shepherd of Hermas and the Didache, hovered near the edge without finally entering. The oldest surviving list, the Muratorian fragment, is usually dated to around 170 and already names most of the twenty-seven books.
Two landmarks close the process. In 367 St. Athanasius of Alexandria, in his 39th Festal Letter, gave the first list that matches the New Testament exactly as Christians hold it today — the four Gospels, the Acts, the epistles, and "besides, the Revelation of John." A generation later the regional councils of Hippo (393) and Carthage (397) ratified the same canon for the churches of North Africa. No ecumenical council ever sat down to legislate the list from scratch; rather, the Quinisext Council "in Trullo" (692) simply endorsed the canon lists the Fathers had already handed down. The canon was received, not decreed.
A fruit of the Church
This history carries a lesson Orthodoxy takes to heart. The Bible did not drop from heaven with a table of contents, and no verse of Scripture lists the books of Scripture. The same Church that preached the Gospel also discerned, over time and by the Holy Spirit, which writings truly carried that Gospel — and that discernment is itself part of Holy Tradition. This is why Orthodoxy does not read the Bible as a book standing apart from the Church, but as the Church's own book, read within her worship and interpreted by her Fathers (more here).
The canon, then, is a fruit of the Church's life, not a foundation stone laid down in advance and independent of her. To trust the Bible, in the Orthodox understanding, is already to trust the community that recognized it — the same community that still gathers around it week by week.