The case I am making is that the traditional calendar was considered to be the universal calendar of the Church, and that no deviation was permitted. The principle evidence that it was considered to be the universal calendar is twofold: the fact that the Church everywhere celebrated on the same calendar, at least by the end of the period of the Seven Councils; and the testimony of the three councils in the 16th century condemning the Papal calendar revision. We only start to hear affirmations of the need for calendar uniformity in the 16th century because before then everyone in East and West followed the same calendar, so it wasn't an issue.
Yes, it is true that in practice, after the First Ecumenical Council determined the calendar and the date of Pascha, some places continued to celebrate on a different calendar and to calculate Pascha differently, but gradually these differences were resolved. Some discrepancies were never resolved, i.e. the different dates for commemoration of Saints in the West. But the trend is universally in the direction of unity, not discord.
I know that the new calendar you use is slightly different from the Gregorian calendar of the West. But I don't accept that the adoption of the new calendar is unrelated to the Western calendar, because the context of the adoption of the new calendar was ecumenism, as is proven by the patriarchal encyclical of 1920, and the simple fact that in practice, new calendarists celebrate most of their feasts with the heterodox, not the Orthodox.
You have asked a very good question. Yes, if astronomical accuracy were the only concern, by which I take it to mean that the date of Pascha should depend upon the astronomical equinox, rather than a conventional equinox, we should all go to the Gregorian calendar, or the revised Julian calendar, for both the Menologion, i.e. the fixed feasts, and the Paschalion, whose dates must depend on a fixed date in the solar calendar. Having the Menologion and Paschalion operate on different calendars introduces a great degree of confusion, as you know. But as you intimate, astronomical accuracy is not the only concern, and in fact the history of the Church's treatment of the question shows that accuracy was considered subordinate to the need for unity in the Church. Moreover, there is one important justification for not changing the Paschalion, which is that revising the calendar pushes our Pascha back on or before the date the Jews celebrate their Passover, and the determination of the calendar at the First Ecumenical Council made it clear that coincidence of our Pascha with the Jewish Pascha was absolutely forbidden.
Below is a long list of evidence for the way the Church has traditionally approached the question, taken from Fr Basil's book:
1. From ancient times, the Church has been aware of the calendar’s
imperfection. For this reason She fixed a conventional equinox which
disregards the astronomical equinox.
2. In 1324, Nicephorus Gregoras determined the calendar’s error with
exactness and submitted a report containing propositions for changing
it; however, nothing came of this.
3. In 1371, the monk Isaacius and Matthew Blastaris approved Gregoras’
calendar and supported it, but the Church showed no interest.
4. During the days shortly before the fall of Constantinople, George
Gemistus proposed new reforms for the calendar, which were likewise
rejected by the Church.
5. In 1582, Patriarch Jeremy II wrote a letter to the Orthodox Church of
Poland, forbidding the use of the new calendar, under the penalty of
6. In 1582, Patriarch Jeremy II wrote a letter to the Doge of Venice,
wherein he shows that the question of the calendar is a matter lacking
in seriousness: “child’s play.”
7. In 1583, there was convened in Constantinople the first Pan-Orthodox
Council to condemn the papal calendar.
8. In 1583, Meletius Pegas addressed himself to Cardinal Julius
Antonius, wherein he shows him the deficiencies of the Gregorian
calendar. At the same time, he wrote the Alexandrian Tome
concerning the celebration of Pascha.
9. In 1584, Patriarch Jeremy II wrote a letter to the Pope of Rome against
the Latin’s arbitrary coup d’etat concerning the calendar.
10. In 1587, the second Council condemning the calendar used in the
West was held at Constantinople.
11. In 1593, the third Council condemning the new calendar was held in
12. In the 1670’s, Dositheus, the Patriarch of Jerusalem (in his work
Concerning Unleavened Bread, p. 539) said: “By the grace of Christ,
from the time of the First Council to this present moment, the sacred
Pascha is always celebrated the Sunday after the Passover of of the
Law, and we have never experienced any confusion which might bring
us to the necessity of making some correction. This was set forth very
well by the Holy Fathers and it shall eternally remain faultless.
Wrongly have the contemporary astronomers of Old Rome removed
ten days from the month of October. More-over, their new calendar
provokes much confusion and many causes for disorder.”
13. In 1827, Agathangelus, the Ecumenical Patriarch, refused to permit
any correction of the so-called “Julian” festal calendar of the
14. In 1895, Patriarch Anthimus VII forbade any discussion of the
question of the calendar.
15. In 1902, the Great Church of Christ rejected the mathematician
Epaminondas Polydore’s memorandum concerning the change of the
16. In 1903 (Feb. 28), the Russian Church issued the following opinion:
“…this change, which disturbs the order that has already been
established and which has been sanctified by the Church during such a
great expanse of time, will indubitably bring about disturbances in the
life of the Church.”
17. In 1903 (June 5), the Church of Jerusalem issued the following
opinion: “Any decision to change the calendar, out of preference for
the Gregorian calendar, will be to the detriment of Orthodoxy.”
18. In 1903 (July 14), the Church of Greece issued the following, opinion:
“…the Julian calendar (hemerologion) is bound together with the
festal calendar (heortologion) of the Church.”
19. In 1903, the Rumanian Church made the following decision: “The
Sacred Synod of the Holy Autocephalous Church of Rumania is of the
opinion and proposes that we abide therein where we find ourselves
today. For it is impossible not to violate the prescriptions of the
canons should we wish to consider some change or reform of the
Julian calendar, with which the Orthodox Church has lived for so
great a time. Besides this, it is not permitted to us to touch even with
our finger the ancient decisions which constitute the glory of our
20. In 1904 (May 12), the Ecumenical Patriarchate issued the following
opinion: “It is praiseworthy and good to keep the Paschalion which
has already been defined and ratified by the ancient practice of the
Church…and it is not permitted to introduce any innovation
concerning it (the calendar)…From an ecclesiastical point of view, we
are in no wise obliged to change the calendar.
21. In 1919, the Church of Greece issued the following opinion: (see,
Bishop Polycarp of Diaulia, ibid., p. 16): “The change of the Julian
Calendar, which change does not offend dogmatic and social
considerations, could be accomplished with the agreement of all the
other autocephalous Orthodox Churches, and especially with the
agreement of the Ecumenical Patriarch, to whom it would be
necessary to entrust the initiative in such an undertaking -- under the
condition that the Gregorian calendar not be adopted, but that a new
calendar be redacted, which would be even more exact scientifically
and free from the deficiencies of the two present calendars, the Julian
and the Gregorian. (It should be noted that one of the committee
members who voted in favour of this position was Chrysostom
Papadopoulos, then an Archimandrite and Professor of Theology at
the University of Athens.)
22. In 1924, the Church of Alexandria issued the following opinion: “#28.
To Gregory, Patriarch of Constantinople. After receiving the telegram
of Your All-holiness, our Sacred Synod was convoked today and
decided the following: We shall abide with the former synodical
decisions and we reject any addition or any change of the calendar.”