Yet another first class delusional structure

That would be Easter, when Christians celebrate the 'resurrection' of Jesus Christ. The fact that it's really a pagan holiday, the vernal equinox or the start of Spring, and derived from the Jewish holiday of Passover, doesn't bear on the nature of the day for Christians.
Constantine I, Roman emperor, convoked the Council of Nicaea in 325. The council unanimously ruled that the Easter festival should be celebrated throughout the Christian world on the first Sunday after the full moon following the vernal equinox; and that if the full moon should occur on a Sunday and thereby coincide with the Passover festival, Easter should be commemorated on the Sunday following. Coincidence of the feasts of Easter and Passover was thus avoided.

Rico says it's nice that all the Christians can use the same delusional structure, no matter what day they celebrate it...