Today, Easter’s date, at least in the Western church, is universally agreed upon. The Sunday after the first full moon after the vernal equinox relates to the dating of Passover. How the equinox is calculated depends on whether the Gregorian or Julian calendar is used – so in modern times, when to observe Easter is complicated for this reason. The second controversy is an ancient one: Passover is based on a lunar cycle, whereas Easter is celebrated on a Sunday. Some ancient Christians would celebrate Easter on whatever day Passover falls, while some insisted upon Sunday recognition because of the resurrection. The Sunday of Passover then becomes the day you celebrate the “Christian Passover” or early Easter.
This divide could even be seen geographically, as the Eastern Mediterranean (modern-day Turkey) celebrated on Jewish Passover, whereas the Western Mediterranean (modern-day Italy) prioritized celebrating on Sunday. This divide was important politically speaking, as bishops across this geographical region were aware of the distinction and argued about who was worshipping and celebrating correctly. One reason this was so important was in order to create distinctions between Jewish and Christian communities, which may explain why Sunday Easter won this particular battle.
This question brings us to the beginnings of anti-Semitism in Christian communities. The arguments surrounding Easter and Passover involved the “Christ-killer” trope, in which Christians blame Jews for the death of Christ – the question of how you celebrated Passover became a distinction made between Christians and Jews.
Which calendar was used (Jewish, Julian, or Gregorian) became crucial to making distinctions between communities. Eastern Christian groups disliked the Gregorian calendar for its western (and papal) priorities and origin. Beyond the issue of when Passover/Easter falls, this was a question of who got to determine how we measured time. Agricultural festivals would have been celebrated at different points by geographically separated people, as crops grow at different rates, rains are expected at different times, etc. With the introduction of historical, calendrical dating, festival celebrations become standardized, which Joel Baden calls “constitutive of community.” The fundamental goal of ritual in the first place is the binding together of people. There is a sense of connection through participation in common rituals at the same time. So while the calendar and complexities surrounding these central holidays divided people and kept groups distinct, they also allowed – and continue to allow – people around the world to celebrate together in community.