The Orthodox Church embodies and expresses the rich spiritual treasures of Eastern Christianity. It should not be forgotten that the Gospel of Christ was first preached and the first Christian communities were established in the lands surrounding the Mediterranean Sea. It was in these eastern regions of the old Roman Empire that the Christian faith matured in its struggle against paganism and heresy. There, the great Fathers lived and taught. It was in the cities of the East that the fundamentals of our faith were proclaimed at the Seven Ecumenical Councils.
The spirit of Christianity which was nurtured in the East had a particular favor. It was distinct, though not necessarily opposed, to that which developed in the Western portion of the Roman Empire and subsequent Medieval Kingdoms in the West. While Christianity in the West developed in lands which knew the legal and moral philosophy of Ancient Rome, Eastern Christianity developed in lands which knew the Semitic and Hellenistic cultures. While the West was concerned with the Passion of Christ and the sin of man, the East emphasized the Resurrection of Christ and the deification of man. While the West leaned toward a legalistic view of religion, the East espoused a more mystical theology. Since the Early Church was not monolithic, the two great traditions existed together for more than a thousand years until the Great Schism divided the Church. Today, Roman Catholics and Protestants are heirs to the Western tradition, and the Orthodox are heirs to the Eastern tradition.
Christians of the Eastern Churches call themselves Orthodox. This description comes to us from the 5th century and has two meanings which are closely related. The first definition is “true teaching.” The Orthodox Church believes that she has maintained and handed down the Christian faith, free from error and distortion, from the days of the Apostles. The second definition, which is actually the more preferred, is “true praise.” To bless, praise, and glorify God the Father, Son, and Holy Spirit is the fundamental purpose of the Church. All her activities, even her doctrinal formulations, are directed toward this goal.
Occasionally, the word Catholic is also used to describe the Orthodox Church. This description, dating back to the second century, is embodied in the Nicene Creed, which acknowledges One, Holy, Catholic, and Apostolic Church. From the Orthodox perspective, Catholic means that the Church is universal and also that she includes persons of all races and cultures. It also affirms that the Church has preserved the fullness of the Christian faith. It is not unusual for titles such as Greek, Russian, and Antiochian to be used in describing Orthodox Churches. These appellations refer to the cultural or national roots of a particular parish, diocese, or archdiocese.
Source: Greek Orthodox Archdiocese of America, http://www.goarch.org/ourfaith/ourfaith7052.