When and why did the great Schism start?
Both the first and third answers are partially correct. The Cannons were important, but were only one factor. The Ecumenical Council was at Nicea, not Nice. The change in the word of that phrase doesn’t include “procedeth”, but rather “proceeds from the Father ‘and the Son'” and it’s called the Filioque clause (Fee Lee O Kway). The Council of Nicea was considered to be infallible and it was declared at the conclusion of the council that all beliefs enunciated at the council were binding on all Christians and that no changes could be made without another Ecumenical council making them lest one be declared anathema. This was reiterated by the 8th Ecumenical Council. This phrase was not included in the Creed by the Councils of Nicea or Constantinople, and the Orthodox Churches consider this inclusion to be a heresy. Most important in its addition is that the Bishop of Rome added this without authority. That was very much a power play and the beginning salvo in a movement to declare that R
