Filioque, a problem for the Eastern and Western Church (1)

The word "filioque" was added by the Western Church as a "fortress protector" of the threat of Arianism, was not clear when and where the insertion is done but at least, the Spanish Church has inserted "Filioque" in the third council of Toledo (589), if not before. From Spain, this inserts the word spread to France and from there to Germany, where it was well received by Karel the Great (Charlemagne), and adopted at the Semi-Iconoclastic council at Frankfurt (749). Great Karel also the first to start a controversy on the issue of "filioque" by accusing the Orthodox (Eastern Churches) as heretics because they say the Creed in its original form (the Creed of Nicea-Constantinople).

It is noteworthy, the Church of Rome (which is very unique with its conservative attitude) continue to use the Creed without interpolation "Filioque" to the beginning of the eleventh century. Even in the year 808, Pope Leo III wrote a letter to Karel the Great, in which stated that, although he personally believes that the Filioque is not doctrinally problematic, but he thought that was a mistake to change the words of the Confession of Faith. Pope Leo III and even then had to write the Creed without the Filioque on a silver plate and placed in the Church of St. Peter (St. Peter's Basilica).

In explaining the doctrine of the Trinity, orthodox churches in the East (whether it is leaning Chalcedonian and non-Chalcedonian) maintain that only one source of divinity, the form of God (metaphor: the Father). So about the eating of meat Sacrificed to idols: we know that "there is no idol in the world," and that "there is no God but one." Indeed, even though there are so-called gods in heaven and on earth (there are, to be sure, many "gods" and many "Lords"), yet for us there is one God, the Father, from whom all things are and for whom we exist, and one Lord, Jesus Christ, through whom all things are and through whom we exist. (1 Corinthians 8:4-6, NAB)

Of one essence is eternal, the Word of God out before all ages (Divine Birth of the Son, John 1:1-3), and with it comes the Spirit of God, too. (John 15:26, "For just as the Father has life in himself, so also he gave to his Son the possession of life in himself.")

So, according to the Gospel text itself there is no parenthesis "and Son". Why the Eastern churches rejected without the slightest compromise on the interpolation "Filioque" is? Even when the Western church in 1439 in Ferrara insertion force "Filioque" as a condition for military aid against the Turks, why the Eastern churches still reject it, until they were then under the control of Islamic rule?