In 1582 Pope Gregory XIII adopted the current Gregorian calendar, which is used in most parts of the world. It is with this calendar that Catholics and other Christians figure the dates for holy days, such as Christmas and Easter. The Gregorian calendar replaced the Julian calendar which was approved by Julius Cesar during his reign before the birth of Christ.
The date of Easter, for example, has long been a source of contention between the Catholic and Orthodox communities worldwide. In places such as the Holy Land, where Catholics and Orthodox live together, this reality can pose a problem.
The Franciscan 'Custos' or Custodian of the Holy Places in the Holy Land explained that this presents a pastoral problem that can be amended. Says Fr. Pierbattista Pizzaballa, "Ecumenism in the Holy Land is not a theological problem, is a pastoral problem. Because all families are mixed families. One part is Orthodox and another Catholic. So we have two different calendars: the Gregorian calendar and the Julian calendar for families.”
To further good ecumenical relations, the Latin Patriarchate of Jerusalem has decided to modify its liturgical schedule so as to be congruent with the practice of the Orthodox churches. This means Easter in the Holy Land will be celebrated on May 5th in 2013 rather than March 31. However, to accomodate pilgrims who come from elsewhere, Jerusalem and Bethlehem will not follow the new calendar.
Said Fr. Pizzaballa, “For Christian families, it's a problem. They want to celebrate Christmas together and Easter together. So the Catholic Church decided to adopt just for Easter, not for Christmas, the Julian calendar in order to allow and permit our Christian families to celebrated Easter together.”
As of 2015, the Latin Patriarchate will adopt the Julian calendar, indefinitively. From that point onwards, Christians will celebrate Easter together, the central celebration of the faith. In Greece, another country where Catholics and Orthodox co-exist, Easter is also celebrated on the same date. So far, there has been no indication from the Vatican that a change in imminent for the rest of the worldwide church.