The word Easter goes back to Eastre, which was the Teutonic spring goddess for whom sacrifices were offered in April. This provoked the faithful to make sure the date of Easter Day could be moved. They didn't want it to coincide with pagan holidays. So the dating of Easter Day was fixed by the Council of Nicea in AD 325 to be "on the first Sunday after the date of the first full moon after the vernal equinox, March 21, except when the full moon falls on Sunday, when Easter is one week later."
While I am completely baffled by that formula, I know 75% of the church's calendar is determined by the date of Easter. As Frank Wilson wrote, "Easter is the axis on which the Christian year revolves." Or as Paul wrote, "If Christ has not been raised, then our preaching is in vain and your faith is in vain" (1 Cor. 15).
In short, without resurrection, there is no Christian calendar. There is no Christianity without the resurrection!
(Robert Kopp, Bethany Presbyterian Church, Loves Park, IL)