The sources of doctrine as defined in the Orthodox Catechism are the Holy Bible and the Holy Tradition transmitted by the Church.
The Church came into being first, and only afterwards, little by little, did the books of the New Testament, the Gospels and Epistles appeared. Moreover, when we take into account how few "books," or manuscripts, there were in those days, and the fact that besides the genuine writings there were other gospels and texts written under the names of the Apostles, it is easy to understand how important the living Tradition of the Church was in safeguarding the true Christian faith. The prime importance of Tradition is plainly shown by the fact that it was not until the fifth century that the Church established conclusively which books in circulation should be regarded as genuinely inspired by God’s revelation. Thus the Church itself determined the composition of the Bible.
It is to the Church, which defined what the contents of the Bible would be, that the Orthodox Christian turns for his/her interpretation of the Bible. It is not merely a question of the authority of the Church; the promise was given only to the pure in heart that "they shall see God." (Mt 5:8) In other words, the truths contained in God’s word are revealed to a person in the right light only insofar as their heart is purified. No individual person has possessed complete purity of heart and hence complete infallibility in interpreting the word of God. However, this gift has been granted to the Church as a whole through the Spirit of truth acting within it. In practice this means that when all or most of the Church Fathers known for their holy lives have been consistent with one another in their explanation of some point of Scripture, it has become truth to the members of the Church. Without such a criterion the authority of the Bible would rest upon the subjective opinion of each individual trying to interpret it. It is our belief that the Bible by itself, without the Tradition as its living interpreter, is insufficient as a source of truth.
The fifteenth chapter of Acts tells of a meeting held by the Apostles, who announced their decision by saying: "It has seemed good to the Holy Spirit and to us..." Similar gatherings of the Apostles’ successors, all the Bishops of the Church, were held from time to time during the first millennium. At these meetings articles of faith were formulated and decisions made on contemporary problems arising in the life of the Church. Seven such ecclesiastical councils have been recognized by the Church as general or ecumenical and their decisions thus recognized as binding upon the whole Church. The first of these synods or councils was held at Nicaea in the year 325 and the seventh in Constantinople in 787.
In addition to the councils recognized as ecumenical, there have been a number of local councils which were important for the whole Church, in both the first and second millennia. For example, a church council was held in Constantinople in 1351 which confirmed the practice of hesychasm, or unceasing prayer of the heart, together with the teaching of St. Gregory Palamas on the uncreated light of the Holy Spirit.
History shows that in the past, meetings which had the authority of Ecumenical Councils have always been called together in the face of a threat to the unity and truth of the Church. Among such threats, for instance, were the Christological heresies concerning the nature of Christ. In our own time the acute problem awaiting a common solution is the so-called diaspora problem, which is weakening the Orthodox witness in the world. In our century the Church has outgrown its own historical garment, so to speak; it has spread over new continents so that it is no longer only the Eastern Church but is Western just as well. This situation calls for recognition of the independence of the new local Churches which have sprung up, especially in America, so that they may participate fully in the common affairs of the Orthodox Churches. Unlike the Roman Catholic Church, the Orthodox Church has no common administrative center; each of the local Churches whose independence has been recognized has its own independent voice in the common affairs of the Church. For historical reasons the Patriarch of Constantinople holds a position of honour among his peers, but he has no authority over the other independent, or autocephalous, Churches.
In Orthodoxy it is emphasized that doctrine and life are two sides of the same thing. Future general councils of the Church will not be concerned with any new doctrines beyond what "the Fathers have decided," but rather with adapting accepted principles of the Church to changing circumstances. This task presupposes a unity of love and peace among the representatives of the Orthodox Churches, who at the Ecumenical Councils included all the bishops of all the Churches, in order that unanimous decisions may be confirmed with the apostolic seal: "It seemed good to the Holy Spirit and to us."