Formal definitions are usually imposed only as a last resort to settle a controversy. Only when a doctrine is challenged is there an acute need to define something precisely. The Council of Trent formally defined the Biblical canon, since only then did a major part of Christendom dare to reject books long read in all the churches. Even at this late date, the Council defines the canon with no more precision than necessary to condemn the new heretical opinion (i.e., that the deuterocanon and parts of Daniel and Esther were not inspired).
The canon of Scripture was defined only by local councils at first. Once a practical consensus had emerged by the fifth century (with the West finally accepting Hebrews and the East finally accepting the Apocalypse of St. John), there was no need for a formal definition of what everyone in the Catholic Church accepted. The Council of Florence listed the Biblical books as a condition of union with the Copts, who include some minor apocrypha (e.g., Letter of Jeremiah, Prayer of Manasseh, Psalm 151).
There has long been a tendency in the ancient churches (even more pronounced in the East) to take a minimalist approach to definitions, precisely because the role of the Magisterium is to safeguard Divine Revelation and not add to it. Dogmatic definitions are a necessary remedy for new opinions and considerations about received doctrine, but they remain subordinate and secondary to the Church’s primary duty to proclaim the Gospel.
The fact that the Holy Apostles and their immediate successors did not see fit to define a specific canon of Holy Scripture, either for the Old or New Testaments, says much about the relation between Scripture and Revelation. The central Revelation of the Church is Christ Himself, and Holy Scripture is but one means of revealing Christ, not even the primary means. The Apostles carried out their divine commission by preaching Christ, and the two who wrote Gospels did so only reluctantly, according to tradition. Most of the New Testament is a haphazard collection of apostolic epistles that were providentially preserved. Some were at first read only in the churches to which they were addressed, and only eventually spread to the rest of the Church. The authority of the New Testament writings was grounded in the personal authority of the Apostles, so any local church that doubted the authenticity of a given epistle would not receive it.
The Apostles never defined an Old Testament canon either, though their writings used the Septuagint, including the deuterocanon, and even some apocrypha. Here the criterion for inclusion was murkier, but from an early date, the Septuagint was the accepted Christian Old Testament, with no distinction among classes of books such as the Jews used (i.e., the Law, the Prophets, and the Writings). In fact, the Septuagint intersperses the deuterocanonical books among the protocanon. Again, there was no formal proclamation, only an acceptance of what had been received, and the Septuagint was used by Christians since the Apostolic age.
All of this points to a thoroughly un-Protestant ecclesiology, where the font of authority, even in defining Scripture, is in the patrimony of the Holy Apostles and the judgments of their successor bishops in the Church. The Orthodox, to this day, consider Holy Scripture to be the Book of the Church, i.e., that which is to be read in church. When the early Patristic writers favor the canonicity of a book, they say as evidence that it is “read in the churches,” clearly making the Church, which is Christ manifest on earth, the source of authority.