Easter Sunday, also called Pascha or Resurrection Sunday, celebrates Jesus being raised from the dead. Though some Christian groups and Messianic Jews continue to worship on Saturday, the Jewish Sabbath, most Christians worship each week on Sunday because of when the resurrection occurred.
His rising from the grave is a cornerstone of the Christian faith. The apostle Paul wrote in 1 Corinthians 15:14 that if resurrection did not happen the preaching of the Gospel and one's faith in Jesus is "worthless."
Those who believe in Jesus regard this event as arguably the most important evidence that He was indeed who He claimed to be, the Son of God, who never sinned and was victorious even over the power of death.
Historically, there have been some Christian groups that rejected celebrating Easter. Following the Protestant Reformation, Anabaptists, Quakers, Congregationalists and Presbyterian Puritans believed that if a church festival or practice could not be found specifically in the Bible it was not to be observed, while other movements like Lutheranism, Anglicanism and Methodism retained it.
Easter Sunday services are often joyful and celebratory, in contrast to the somber, penitential days and 40-day season of Lent that preceded it.