Easter Day
The most important day in the Christian Year is Easter Day. Unlike most other days in the Christian Year, the date on which Easter is celebrated depends on the cycles of the lunar calendar in conjunction with the equinox. In addition to Easter Day itself, there are other days in the Christian Year whose date is dependent on the date of Easter: Ash Wednesday, Maundy Thursday, Good Friday, Easter Eve, Ascension Day, and The Day of Pentecost. These all are linked, along with some other less important days, by the seasons of Lent, Holy Week, and Easter.
The key factor is the feast of Easter itself. The early church celebrated the resurrection each Sunday, that is, in a weekly commemoration of the event (Acts 20:7), rather than in an annual festival. Despite the connections between Christ’s death on the cross and the Passover, there appears to have been little interest in Christian circles in an annual commemoration of the death and resurrection of Jesus until the second century. Nor was there agreement in the church over precisely when Easter should be celebrated, beyond the fact that it should be at the time of the Passover, as clearly attested in the New Testament. There was a controversy in Rome at the time of Pope Victor (189-198) between some Christians from Asia Minor, who celebrated Easter on 14 Nisan, the day the Passover lambs were killed, and the remainder, who celebrated it on the Sunday after the Passover, assimilating the annual commemoration to their weekly celebration. 
The majority of the churches followed the custom of the church in Rome and observed Easter on the appropriate Sunday after Passover, as calculated by the Jewish lunar calendar. There were considerable complications, however, in relating the lunar calendar to the various solar calendars available. The Council of Nicea in 325 advocated following the Alexandrian calculations, which provided the familiar rule that Easter is celebrated on the Sunday after the first full moon after the (northern hemisphere) Spring equinox. That did not end the difficulties, as adjustments to the calendar in later centuries led to differences between churches who adopted the reformed Gregorian calendar in the sixteenth century and those who continued to follow the old Julian calendar. This can still lead to differences in the date of Easter, particularly between some of the Orthodox Churches and the rest of the Christian tradition.
The observance of Easter in the early church was comparatively simple: a fast of a few days, an all-night vigil of prayer, and a concluding eucharist. Central to this, of course, was the recounting of the stories from all four Gospels of the succession of events from the Last Supper to the resurrection of Jesus. So, the essential components were fast, vigil and feast. The Saturday night spent in prayer was probably modelled on the Passover tradition, and the fast was an act of preparation. The Sunday eucharist both ended the fast and vigil and introduced the feast that followed.
In the third and fourth centuries, the celebration of Easter developed significantly, into something close to what we now have. In particular, as Good Friday developed its distinctive character, Easter came to mean the feast of the resurrection. From early in the church’s history, the links made by Paul between the death and resurrection of Christ and the sacrament of baptism meant that Easter soon became the pre-eminent time for the administration of baptism. The lights that were necessary for the all-night vigil were soon connected with the idea of Christ as our light, and the fairly obvious link between this and the celebration of the resurrection produced various songs of Easter praise, such as the Exsultet, which accompanied the lighting of the new fire and the lighting of a Paschal candle or candles. It is not certain when special ceremonies surrounding the lighting of a Paschal candle developed, but the evidence points to the fourth century. The vigil that followed comprised readings, mainly from the Old Testament, psalms and prayers.
Much of this will be familiar, as it is the pattern adopted by many churches, in which the sequence of Easter candle, vigil, baptism or the renewal of baptismal vows, and eucharist is followed. The Easter (Paschal) candle is customarily inscribed with a cross, having an alpha and omega at the top and bottom, symbols of the five wounds of Christ at the ends of the arms and the centre, and the present year on either side of the upright. Much of this is a recovery of the primitive emphases of Easter, which had undergone considerable modification and corruption from the early Middle Ages. In effect, the vigil became truncated or completely ignored, and the ceremonies associated with fire and light were observed earlier and earlier on the Saturday. They then suffered from the forbidding of any celebration of the eucharist after midday on the Saturday (1556), and from the days of Holy Week no longer being days of obligation (1642).
The central celebration of the eucharist on Easter Day was always the one that ended the all-night vigil in the very early church, or one that occurred as early as possible on Easter Day itself. As the festival developed, it was prolonged in various ways. When the vigil ended with the eucharist, there grew up, at least by the late fourth century, the custom of a second eucharist in daylight hours. Egeria, a pilgrim to Jerusalem towards the end of the fourth century, mentions this. Later developments included a more elaborate form of the Vespers for Easter Day and other customs.
For Liturgical Use
In this great celebration, we gather up all that has happened, from the birth in the manger to the great events of these last three days. In the Last Supper, Jesus offered his disciples a sign of his presence with them always. Let us, in this eucharist, join with the countless throngs down the ages who have rejoiced in the triumph of God’s love, won for us on the cross and proclaimed here in the greatest festival of all, as new life is made manifest in Christ.
Sentence, Prayers and Readings as in A New Zealand Prayer Book - He Karakia Mihinare o Aotearoa, page 591-593.