It was writers at Charlemagne’s court who first made the Filioque into an issue of controversy, accusing the Greeks of heresy because they recited the Creed in its original form. But Rome, with typical conservatism, continued to use the Creed without the Filioque until the start of the eleventh century. In 808 Pope Leo III wrote, in a letter to Charlemagne, that, although he himself believed the Filioque to be doctrinally sound, yet he considered it a mistake to tamper with the wording of the Creed. Leo deliberately had the Creed, without the Filioque, inscribed on silver plaques and set up in St Peter’s. For the time being Rome acted as a mediator between the Franks and Byzantium.
It was not until 860 that the Greeks paid much attention to the Filioque, but once they did, their reaction was sharply critical. The Eastern Church objected (and still does) to this addition to the Creed, for two reasons: (1) the Creed is the common possession of the whole Church and, if any change is to be made in it, it must be done by an Ecumenical Council. The west, in altering the Creed without consulting the east, is guilty, as one author puts it, of moral fratricide – of a sin against the unity of the Church; and (2) most of the Easter Church believes that the Filioque to be theologically untrue. They hold that the Spirit proceeds from the Father alone, and consider it a heresy to say that He proceeds from the Son as well. There are, however, some Orthodox who consider that the Filioque is not in itself heretical, and is indeed admissible as a theological opinion – not a dogma – provided that it is properly explained. But even those who take this more moderate view still regard it as an unauthorized addition.
It is all about how we understand the life of the Trinity and the roles that each Person plays within the Trinity. Of course this is all in accord with human thought and not something that God has revealed to us. The role of the Father is to “beget” the other two Persons. He is the Creator. However, since all Three Persons in the Trinity are equal and one, this, in reality, is a mute point.
Besides these two major issues (i.e.. the role of the Pope and the Filioque, there were certain lesser matters of Church worship and discipline which caused trouble between east and west: the Greeks allowed married clergy, the Latins insisted on priestly celibacy; the two sides had different rules of fasting; the Greeks used leavened bread in the Eucharist, the Latins unleavened bread.
Since we are still living it, I shall continue to present ideas about the Great Schism