Paradosis (delivering):
In founding the Church, Jesus Christ has used verbal preaching that was testified by the Holy Spirit, and preaching gets delivered. The term "tradition" which comes from the Latin tradition is sometimes used but does not indicate the accurate meaning, while the Greek term “paradosis” does.
So was and is the life of the members of the true Church: receives and delivers, oral delivery, and then the written delivery for pastoral reasons, when the Apostles could not leave some places where they were.
Paradosis are: books of the Bible, the Faith Creed, decisions of the Ecumenical Councils, writings and behaviors of the apostles and saints and Church Fathers, the ecclesiastical laws, the liturgical books, and sacred icons, ie everything the Orthodox Christianity has expressed through ages with doctrine, Church organization, worship and art.
These are the basic elements that form the Paradosis, which cannot be separated from each other since the Holy Spirit speaks through them all. They form an integrated unit, while each element is understood in the light of the other elements. Hence, the Orthodox Christian Church does not reply on the Bible alone, but on the gospel preached by the apostles and delivered to the Church.
The Development of Doctrine:
The Orthodox Church does not endorse the view that the teachings of Christ have changed from time to time; rather that Christianity has remained unaltered from the moment that the Lord delivered the Faith to the Apostles (Matt. 28: 18-20). She affirms that "the faith once delivered to the saints" (Jude 3) is now what it was in the beginning. Orthodox of the twentieth century believe precisely what was believed by Orthodox of the first, the fifth, the tenth, the fifteenth centuries.
Orthodoxy recognizes external changes (e.g., vestments of clergy, monastic habits, new feasts, canons of ecumenical and regional councils, etc.), but nothing has been added or subtracted from her Faith. The external changes have a single purpose: To express that Faith under new circumstances. For example, the Bible and divine Services were translated from Hebrew and Greek into the language of new lands; or new religious customs arose to express the ethnic sensibilities of the converted peoples, etc.; nevertheless, their has always been "one faith, one Lord, one baptism".
Faith and Reason:
Following the Holy Fathers, Orthodoxy uses science and philosophy to defend and explain her Faith, and does not build on the results of philosophy and science. The Church does not seek to reconcile faith and reason. She makes no effort to prove by logic or science what Christ gave His followers to believe. If physics or biology or chemistry or philosophy lends support to the teachings of the Church, she does not refuse them. However, Orthodoxy is not intimidated by man's intellectual accomplishments. She does not bow to them and change the Christian Faith to make it consistent with the results of human thought and science.