The practice of the proclamation dates from a time when calendars were not too readily available. It was necessary to make known the date of Easter in advance, since many celebrations of the liturgical year depend on its date. The number of weeks that follow Epiphany, the date of Ash Wednesday and the number of Sundays that follow Pentecost are all computed in relation to Easter.
[If you would like some more detail of the history of the Proclamation head over to New Liturgical Movement.]
Although calendars now give the date of Easter and the other feasts in the liturgical year for many years in advance, the Epiphany Proclamation still has value. It is a reminder of the centrality of the resurrection of the Lord in the liturgical year and the importance of the great mysteries of faith which are celebrated each year. This beautiful proclamation puts everything into perspective. Every liturgical celebration of the Church finds its authentic meaning in the Paschal Mystery, even Christmas. The Paschal Mystery was precisely why the Eternal Son of the Father, the Eternal Word, deigned to leap down from heaven and become incarnate in the womb of the Blessed Virgin Mary. He was born in time so that He could give His flesh for the life of the world.
The season of Christmas ends with the celebration of the Baptism of the Lord. As the season draws to an end, the solemnity of Epiphany offers an opportunity to proclaim the centrality of Christ's paschal mystery: dying he destroyed our death and rising he restored our life.
The Easter Triduum of the Passion, Death and Resurrection of Christ is the culmination of the entire liturgical year and the solemn proclamation should be made after the homily or after the Prayer after Communion on the Solemnity of the Epiphany of the Lord on January 6th.
Below is the Proclamation with the dates for 2018 as per the Irish Liturgical Calendar.
that, as we have rejoiced at the Nativity of our Lord Jesus Christ,
so by leave of God's mercy
we announce to you also the joy of his Resurrection,
who is our Saviour.
On the fourteenth day of February will fall Ash Wednesday, and the beginning of the fast of the most sacred Lenten season.
On the first day of April you will celebrate with joy Easter Day, the Paschal feast of our Lord Jesus Christ.
On the thirteenth day of May will be the Ascension of our Lord Jesus Christ.
On the twentieth day of June, the feast of Pentecost.
On the third day of June, the feast of the Most Holy Body and Blood of Christ.
On the second day of December, the First Sunday of the Advent of our Lord Jesus Christ,
to whom is honor and glory for ever and ever.