Can you tell me a little bit more about the ecumenical councils? When exactly were those formed? I guess I'm not fully clear why they're invalid or why they wouldn't be binding on the Church before all the schisms and splits (I assume those councils were before any split, correct?)
What the Orthodox Church (and Catholic Church for that matter) tends to portray is this single monolithic set of seven councils, that all True Christians (i.e. Orthodox) have always recognized as authoritative, since the dawn of Christianity. That's not how they really went.
The councils were a lot like denominational conventions are today -- pastors got together to discuss issues that were arising in their churches, to talk about how to deal with the problems brought on by persecution, etc. We have this idea that they were some grand royal-type arrangement. We're talking about ordinary pastors who were doing their best to be faithful to their congregations and the Scriptures, meeting to deal with problems and doctrinal concerns and heresies and to encourage and promote the unity of the church. They were patterned after the Jerusalem Council which is mentioned in Acts 15, when the apostles met to discuss the management of the churches and the issue of circumcision -- and when Paul rebuked Peter for giving in to the Judaizers.
The "First Ecumenical Council," as it's called, was the council of Nicaea in 325. Constantine asked for it to be called (probably at the urging of his pastor) to settle some disagreements about the nature of Christ and the trinity, because a pastor named Arius had been teaching his church that Jesus was a created being who was not fully divine. Since that's not what the Scriptures teach, the council asked him to repent, and he refused. The important thing to remember is that the council didn't decide that Arius was wrong and his opponent Athanasius was right -- they recognized that Arius's teachings were out of line with what Christians have always believed, and so they called him to repent, and when he refused, they removed him from his position as pastor of his church in Alexandria and excommunicated him. We get the Nicene Creed from this council, which is just a clear statement of the beliefs Christians have always held.
The next council was the council of Chalcedon, which addressed similar issues with the humanity of Jesus. Again, they weren't deciding that Jesus was human; they were recognizing what the Scriptures teach.
There is general agreement among Eastern Orthodox on most of the Seven Ecumenical Councils. But some Orthodox recognize certain ones that other Orthodox don't -- so it's kinda 6 + one or the other, or 6 + 2. Also, some councils were considered ecumenical (universal) at the time but were later rejected -- usually because a so-called ecumenical council would promote heresy and then would be hard-core corrected a few years later.
There were schisms between the Assyrian church and Orthodox, and Oriental Orthodox and Orthodox in the midst of the councils. The "Great Schism" didn't happen until the 11th century, but there had been major trouble brewing for about 400 years between the East (Orthodox) and the West (Roman Catholic). The Great Schism was kinda the last, "Oh yeah? Well I excommunicate you TOO! Take THAT!"
For me as a Protestant, there are two major areas of disagreement with the Orthodox (and Catholic) view of the Councils.
1. The creeds. Catholics and Orthodox see creeds (which came out of the councils) as authoritative because the council wrote them. I see the creeds as helpful, but not authoritative, summaries of what the Scriptures teach and thus what Christians have always believed. The Councils didn't "come up with" this statement of belief, they just wrote it down in a clear way to prevent heretics from feeling like they could teach something contrary to the Scriptures. Creeds are like mini-systematic theology texts. I don't take a Systematic textbook and call it perfectly authoritative, but I sure do find it helpful in organizing what the Bible says on a particular issue. That's all creeds are -- condensing down the essentials of the faith into a few easy-to-learn paragraphs. There's pretty good consensus that the organization and content of creeds came from "baptismal formulas" -- sort of like interviews: what do you believe about God the Father? What do you believe about Christ? What do you believe about the Holy Spirit and the church and the resurrection, etc.? -- to test the beliefs of a candidate for baptism.
2. The nature of the councils. Catholics and Orthodox look at the councils and say, "Those people got together to DECIDE Christian doctrine. Without them, we wouldn't KNOW what true Christian doctrine was!" Baloney. The Scriptures contain everything we need for life and godliness, and these godly pastors and overseers knew that. That's why they used the Scriptures to repudiate heresy and keep the church as a whole pure. That's why they used the methods of the Bible to exclude people who didn't teach in accordance with the doctrines all Christians have always believed.
Part of the reason we struggle to get our minds around these councils, I think, is that we see titles like "bishop" and think Oh, that sounds very official and serious! -- but that word translated as "bishop" by some Eastern Orthodox and Catholics is the word "presbuteros," which is the word we translate as "elder." So we are literally talking about pastors or elders, plus regional and national leaders, getting together to address problems and promote unity, not a bunch of Cardinal-types meeting to decide whether or not we should believe that Jesus is fully man and fully God. They simply affirmed what the Scriptures already taught.
There's such a temptation to desire that someone in an authoritative position would just tell us what the Scriptures mean. But two things about that. First, pastors are just as fallible as we are -- they're not our "high priests" who intercede for us, Jesus is, nor are they our perfect guide to God's word. The Holy Spirit is. Second, whenever the Scriptures are taught or prophecy or words of knowledge are spoken, Paul (for example) tells us to test what is right in what they're saying. He doesn't say, "If I come and preach to you, you better just accept what I way because I'm an apostle!" He instead commends the Bereans, for example, because when he came to them, they earnestly searched the Scriptures to see if what he said was true. We're never supposed to just go along with what a Christian leader says without being certain that they are in line with what we know to be true in God's word.
Look, nobody would have the nerve to say, "Last year's Southern Baptist Convention in Indianapolis is perfectly authoritative on the same level as Scripture for all Christians everywhere, and anyone who rejects its decisions is anathema." But for some reason we're tempted to think that a gathering of fallible humans can make perfect and perfectly authoritative declarations just because the gathering took place 1700 years ago. It's a crazily false view of history. We are no more or less jacked-up than they were. They had their hidden sins, their blind spots, their mistaken theologies -- for instance, the oldest creed we have is the Apostles Creed (from around the 2nd Century) and I disagree with one of the lines when it says that Jesus "descended into hell." I don't think the Scripture indicates that Jesus went to Hell! The worship of Mary began as early as the 4th century. Does that make it right? No way!
We get this notion in our heads that these "great men of old" had it together in a way that we don't, but that just doesn't reflect the picture of humanity that we get in the Scriptures. Luther hated Jews. Calvin allowed the state to execute heretics. Augustine thought sex was evil and abstinence was the only holy path for "serious" Christians. The first Baptists turned into political revolutionaries. Everyone, even those halo-sporting council guys, gets things wrong. Maybe God allows that to keep us humble. Maybe he allows it so we'll long for Christ's return and the perfect unity of God's church. I don't know. But it's the reality.