In 325 AD Constantine, the emperor of Rome, who was considered both a pagan god and a Christian saint, set the date for Easter. It should be remembered that Constantine worshiped Mithra the Persian sun god before his conversion and worked to meld the two religions (Mithraism and Christianity) together. If you have studied history about this man, you know that he was extremely evil. He murdered members of his own family, and he refused to be baptized until his deathbed because he knew he would continue to live in sin. And it was this very Emperor Constantine, in the Council Nice, who ordered all churches to celebrate the Resurrection of Christ on Easter Sunday.
The ancient church had celebrated the Resurrection during the Passover [Nisan 14], which could fall on any day of the week, but the churches near Rome had abandoned the practice because they hated the Jews, and fixed the date to the first Sunday after the first full moon of spring. They also called the celebration 'Easter', after the pagan goddess of spring. All of this is verified by the following quote from the Encarta Encyclopedia:
"An important historical result of the difference in reckoning the date of Easter was that the Christian churches in the East, which were closer to the birthplace of the new religion and in which old traditions were strong, observed [the Resurrection] according to the date of the Passover festival. The churches of the West, descendants of Greco-Roman civilization, celebrated Easter on a Sunday.
"Constantine the Great, 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.
"The name [Easter] probably comes from Eastre, the Anglo-Saxon name of a Teutonic goddess of spring and fertility, to whom was dedicated a month corresponding to April. Her festival was celebrated on the day of the vernal equinox; traditions associated with the festival survive in the Easter rabbit, a symbol of fertility, and in colored Easter eggs, originally painted with bright colors to represent the sunlight of spring, and used in Easter-egg rolling contests or given as gifts..." (Encarta Encyclopedia, article: Easter).
The following is an actual quote from Constantine showing that at the heart of the Sunday issue was Rome's hatred for the Jews.
"And truly, in the first place, it seems to everyone a most unworthy thing that we should follow the customs of the Jews in the celebration of this most holy solemnity, who, polluted wretches! having stained their hands with a nefarious crime, are justly blinded in their minds. It is fit, therefore, that rejecting the practice of this people, we should perpetuate to all future ages the celebration of this rite, in a more legitimate order, which we have kept from the first day of our 'Lord's' passion even to the present times. Let us then have nothing in common with the most hostile rabble of the Jews" (Council of Nicea, pg. 52).
So we see, 'Easter' is not a biblical celebration. The apostles never celebrated, nor did the church for the first three centuries. It is an invention of Constantine the Great, who worked vigorously to unite the pagan religions of Rome with Christianity. His invention still exists, sitting atop the Seven Hills of Rome.