The First Ecumenical Council of Nicaea, called for by Emperor Constantine, met in 325. The job of the council was to iron out dogmatic differences between the formerly fragmented Christian communities in the Roman Empire. For the needs of this article, I will bring up only two of the many important decisions that came out of this Council. The first ruling confirmed the power of metropolitan sees (later called Patriarchates), namely cities that had authority over areas outside their province. The original five Patriarchs sat in Rome, Constantinople, Alexandria, Antioch, and Jerusalem. Rome was considered first in power among these metropolitan sees.
The second ruling concerned a unified confession of faith, known today as the Nicene Creed. This was not the final time the Nicene Creed would be ruled upon. It is, however, the first attempt to solidify Christian belief in the Roman Empire.
While there were other theological differences between the East and West, the precedence of metropolitan sees and the contents of the Nicene Creed are paramount in understanding the Great Schism. As Rome’s power waned, Constantinople’s (originally christened Nova Roma, or New Rome) increased greatly. The Eastern Patriarchs saw learning slowly decline in the Western Empire, as it was constantly mired in war and led by petty, squabbling nobles. They began to question why the Bishop of Rome, so reduced in power, should hold sway over them. The Patriarchate of Constantinople sought to expand its influence, specifically over the other three Eastern Patriarchates, thus vexing Rome, who saw itself as the supreme head of the Church.
The second, and probably most theologically relevant, reason behind the split was the inclusion of the filioque in the Western version of the Nicene Creed. Filioque is Latin for “and from the Son” and was added to the Creed in the following way: “We believe in the Holy Spirit, the Lord, giver of life, who proceeds from the Father and from the Son…”
