In what way are the early church councils "authoritative" for Eastern Orthodox Christians? Do the decisions of these councils have the same status as Scripture? Would the Eastern Orthodox reject the Protestant idea of Sola Scriptura?
First of all, the Eastern Orthodox Church does not give all church councils equal status. The church does, however, give special prominence to the seven Ecumenical Councils that took place between 325 and 787, representing Christians throughout the Roman Empire. These councils addressed central issues related to the meaning of salvation through the union of the divine and human natures of Christ, and gave us such definitions of Christian faith as the Nicene Creed.
But we make a distinction between a council's decisions and the whole church's reception, or acceptance, of a council's decision. Just because a church council has spoken does not mean it has authority to determine truth. How do we know if a council is genuinely voicing the will of God? There are various external criteria that can indicate the potential presence of the Holy Spirit—such as the number of bishops present from various geographical regions—but none of these criteria is conclusive on its own. No council's decision carries binding force on Orthodox Christians until the communities of faith and their bishops in communion with each other receive/accept that decision. At a true Ecumenical Council, the bishops witness to the apostolic truth, and that witness is subsequently welcomed by the assent of the whole people of God.
Historically, this process took place at various times and in various ways. For example, the conclusions of the Council of Constantinople (381) show that the earlier Council of Nicaea (325) had more or less by that time been accepted by the churches. But Rome did not count the Council of 381 among the Ecumenical Councils until 517. And the seventh Ecumenical Council (787) was not generally received in the West before the eleventh ...