How did it come about that there is a difference in dates for celebration of this most important of Christian holidays?
The celebration of Pascha was instituted by the first generation of Christians, by the Church of the Holy Apostles. Their Epistles, found in the New Testament, bear witness to this. However, during the earliest centuries of the Christian era, there was not yet absolute unity of practice as to the day upon which Pascha, the Resurrection of Christ ,should be celebrated. In the Christian churches of Asia Minor, where there were many Jews who had come to believe in Christ, the feast of Pascha was celebrated on the Jewish Passover, i.e. on the 14th day of Nisan, the first month of Spring. Western Christians, for whom Rome, capital of the Empire, was already a spiritual center in apostolic times, were largely converted pagans. It seemed to them inappropriate to celebrate Christian Pascha together with the Jewish Passover, since Christ’s Resurrection occurred after the Jewish Passover. Thus, in Western Churches there had already developed the tradition of celebrating Pascha on the first day after the first full moon of Spring. The two variant observances of Pascha, Eastern and Western, existed until the First Ecumenical Council, held in the city of Nicaea in Asia Minor in 325 AD, and attended by representatives of all of the local Christian churches, both East and West, decided on the day of celebration for Pascha. According to the decision of the Council, Christian Pascha must be celebrated on the first Sunday after the first full moon of the Spring, but always after the Passover of the Jews. The Eastern Church to this day strictly observes these rules set down by the first Ecumenical Council. The Western Church in its historical development has retained only the first part of this decision - to celebrate Pascha on the first Sunday after the first full moon of Spring; it no longer accords significance to whether Pascha is celebrated during or after the Passover of the Jews.
Archpriest V. Potapov
April 1998