"In 1583, however, Pope Gregory XIII undertook to "reform" the traditional Paschalion in defiance of the Nicean tradition. He, not unlike the modern New Calendarists, argued that the history of the Church provided him with sufficient precedent to make these necessary corrections in a calendar that was steadily loosing time. Gregory invited Patriarch Jeremias II of Constantinople to join him in the adoption of his "new style Julian Calendar." His Beatitude convoked the Synod of Constantinople in the same year in order to make a response to the papal innovation. Patriarch Sylvester of Alexandria was in attendance. This Synod condemned the Gregorian reform. Jeremias dispatched an encyclical to Orthodox Christians in every land, commanding them under penalty of punishment not to accept the new Paschalion or the new calendar. The decree was also signed by Patriarch Sylvester and Patriarch Sophronius of Jerusalem.
Four years later (1587), another Synod was held in Constantinople in the presence of the same Jeremias, along with the new Patriarch of Alexandria, Meletios Pegas, and Sophronius of Jerusalem. Again, they rejected the papal revision as "perilous and unnecessary, being the cause of many dangers." The third condemnation of the new Paschalion/calendar occurred at the Synod of Constantinople in 1593. In its 8th canon, the Synod proclaimed "the Latin innovation regarding the celebration of Pascha" to have violated the holy Tradition of the Church. Anyone, it solemnly declared, who presumes to overthrow the definition of "the holy Fathers concerning the holy Feast of the saving Pascha is excommunicated and repudiated by the Church of Christ." It was signed by the Patriarchs of Constantinople, Antioch, Jerusalem, Alexandria and the plenipotentiary of the Russian Church. Jeremias added these terrible words, "He who does not follow the customs which were decreed by the seven holy Ecumenical Councils, which have ordained that we should observe the holy Pascha and Menologion, but prefers to follow the Paschalion and Menologion of the Pope’s astronomers, and opposing himself to all these things, wishes to overturn and destroy them, let him be anathema, and outside the Church of Christ and the assembly of the Faithful…" (quoted in Fr Basil Sakkas, "The Calendar Question," Orthodox Life, XXII, 5 [1972], 20-21). The decision of this Synod was affirmed subsequently by Patriarchs Dositheus of Jerusalem (17th c.) and Cyril V of Constantinople (18th c.). The judgments of these post-Byzantine hierarchs have been universally accepted by the Church, along with the verdict of Patriarch Jeremias.
The Orthodox Church not only reaffirmed her paschal tradition in the 16th century but her calendar of moveable and immovable feasts and fasts dependent on it. The Patriarchs also reaffirmed that no one and no group may usurp the authority of the Church’s ecumenical councils. Their canons may not be revoked. They also demanded that this feast, more than any other sacred and universal custom, demands an external unity among all the local churches as the great sign of their internal unity. Pascha is the "feast of feasts" for which all others exist; it is not only the promise of deliverance from the devil, sin and death, but of deification (theosis). Therefore, to alter the day and season of its celebration, save by the Will of the Holy Spirit Who established it ("it seemed good to the Spirit and to us"), is to invite "many dangers." Finally, to replace the traditional Calendar with another for reasons not approved by the whole Church and by means which involve ends not consistent with the Orthodox understanding of Tradition is to change the Church herself. In a word, the Calendar has evident ecclesiological implications.
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I would hate to try to add to that, it seems to get the point across and I don't have any resources to find out anything more, sorry.