What Is the Orthodox Christian Church? (p.3)
It should be carefully noted that through all this dissension, it was the church of Rome, now ruled autocratically by its pope, that departed from the doctrines and practices established by the united Church in the first centuries of her existence. The Orthodox Church remained faithful at that time, and to this day, to the decisions of the Seven Ecumenical Councils and to the conciliar form of government handed down from the Apostles.
As the Middle Ages progressed, the Roman Church departed farther from its theological roots and became more and more corrupt in its leadership. The abuses attacked by the Protestant reformers were never to be found in the East. Unfortunately, instead of returning to the true Church as it still existed in the East, the reformers consulted only their own consciences and personal interpretations of Scripture. As a result, they discarded much that was good along with what was bad, and even more tragically, established the precedent of individualistic Christianity, which has resulted in the fragmentation of modern Christendom into thousands of denominations. The reformers, in rebelling against the authority of the pope of Rome, effectively created a situation in which every believer has become his own "pope."
Meanwhile, the Orthodox Church had troubles of its own, from external sources rather than internal. In the seventh century, what began as a Christian heresy mixed with elements of Arab paganism grew into a massive political as well as religious threat to Christendom-Islam. In accordance with the Koran's mandate of jihad or religious conquest, the Moslems began conquering territory across North Africa to Spain, and throughout the Middle East. The Byzantine Empire was unable to hold out against this onslaught. Eventually the powers of Europe decided to intervene and launched the Crusades, to wrest back the Holy Land from the hands of the "infidels." But relations with the Orthodox Church had so far deteriorated by this time that the Roman Catholics regarded the Orthodox as just as much "infidels" as the Moslems. The Christians of the East became the object of the destructive fury of the Crusaders along with their Moslem persecutors.
After centuries of battling both Moslems and Europeans, losing territory bit by bit, the last remains of the Byzantine Empire fell to the Turks in the fifteenth century, and Christianity became again a persecuted religion. The cities of the four ancient Eastern patriarchates were now all under Moslem control. Fortunately, Orthodox Christianity had spread before this time into many surrounding territories, and new national churches, some of them patriarchates, had been established in lands north and east of Byzantium. The Russian Slavs had been converted in 988, and by the fifteenth century Orthodox Russia was building a powerful empire that was ready to take over as the secular protector of the Faith. The monks of Mount Athos (a peninsula in the Aegean Sea completely devoted to Orthodox monasticism since the sixth century) also were able to escape Turkish domination, and it was largely they who preserved the spiritual heritage of the Church.