Actually, I've always understood that this clause "after the Jewish Passover" is not in the original Nicene formula and is a actually a misinterpretation of the Nicene formula that became quite prevalent in the Eastern Church. The stipulation as I understand it is that Pascha must be celebrated after the vernal equinox, never before as the Jews were wont to do. Now that it's possible for the Jewish Passover to fall after the second full moon of spring, which actually happened a few years ago, do we continue to insist that following after the Jews means we also have to celebrate Pascha after the second full moon of spring?
It is actually the Jewish Nomicon
("legal") Passover which Canon VII of the Apostolic Canons refers, that is, the date of Passover as commanded by God in Exodus 12, which is the 14th day of the first lunar month of the Jewish Calendar.
Canon VII states that:If any Bishop, or Presbyter, or Deacon celebrate the holy day of Pascha before the vernal equinox with the Jews, let him be deposed.
Note that the Canon mentions nothing about the Full Moon. The only two criteria which the Canon mentions are the Vernal Equinox and the Jewish Passover. Our familiar formula for calculating Easter (the first Sunday after the first full moon after the vernal equinox) is not actually spelled out in the Canon. The Canon simply says that Pascha must fall after the Vernal Equinox and not be celebrated with the Jews. And the reason for this is not Anti-Semitism, but rather, because the Nomicon Passover is the Type
and the Christian Pascha is the Antitype
, and the type should precede the antitype.
The moon's cycle is 29 days and it waxes from the New Moon to the Full Moon for 14 days, then wanes from the Full Moon to the New Moon for 14 days. The Nomicon Pasover which, although is calculated on a lunar calendar, falls on the first vernal full moon since the New Moon marks the beginning of the Lunar Month and the Passover was eaten on the 14th day of the first month- which, of course, was the first Full Moon of the Jewish Year (Exodus 12:6).
Thus, our calculation for Pascha is actually "the first Sunday after the Jewish Nomicon Passover"
based on Canon VII of the Apostolic Canons. Every 300 years, the Jewish Nomicon Passover falls on a Sunday, and on those years, we celebrate Pascha on the following Sunday.
The footnotes to this canon in the Pedalion (page 9) are interesting:
Regarding the finding of Easter an excellent rule, and one which could not be any better, says Matthew Blastaris, was devised and published the holy First Ecumenical Council. in accordance with c.I of the council held at Antioch: which rule is not to be Found in the canons of the First Ecumenical Council, but is is found, according to Balsamon, in its minutes. It is still preserved in the work of Matthew Blastaris, and printed in the holy Gospels and in many other books. Leaving, therefore. exact knowledge of this Paschalion to be learned by itself and separately by those of our own Church who are specially occupied with the study of the Paschalion, we confine ourselves in the present footnote to stating that there are four necessary factors to be sought in connection with the date of our Easter. The first is that Easter must always be celebrated after the occurrence of the vernal equinox. Second. that it must not be celebrated on he same day as the legal Pesach (or Passover) of the Jews. (These two factors are ordained by the present Apostolical Canon VII). Third, that it is not to be celebrated simply and indefinitely after the vernal equinox, but alter the first full moon of March that happens to occur after the equinox. And fourth that it must not be celebrated on the first Sunday that comes after the full moon. (These two, factors arc dcrived from tradition. and not from any canon.)
Hence, in order for these four conditions to be observed equally throughout the inhabited earth, and for Christians to celebrate holy Easter at the same time and on the same day, and in order to escape from the necessity of consulting astronomers and synods every year, the God-wise and God-learned Fathers framed the rule concerning Easter.
Note, however, that on account of the irregularity of the moon's motion, the fourth condition is not always kept but is sometimes violated, because of the fact that, according to the same Blastaris, every three hundred years, two days after the first full moon, the legal Passover happens to occur on a Sunday. These two days which are left over on account of this anomaly when added, sometimes exceed the first Sunday that happens to occur after the full moon in March, on which Sunday we celebrate Palm Sunday, and observe Easter on the following Sunday.