Thanks to Old St. Patrick's Cathedral Bulletin for the following:
The Feast of the Divine Mercy or Divine Mercy Sunday falls on the Octave of Easter (the Sunday immediately following Easter). It is dedicated to the devotion to the Divine Mercy promoted by St. Faustina, and is based upon an entry in St. Faustina's diary stating that anyone who participates in the Mass and receives the sacraments of confession and Eucharist on this day is assured by Jesus of full remission of sins.
According to the notebooks of Saint Faustina, Jesus made the following statements about this day: "On that day the very depths of My tender mercy are open. I pour out a whole ocean of graces upon those souls who approach the fount of My mercy. The soul that will go to Confession and receive Holy Communion shall obtain complete forgiveness of sins and punishment. On that day all the divine floodgates through which grace flow are opened. Let no soul fear to draw near to Me, even though its sins be as scarlet. My mercy is so great that no mind, be it of man or of angel, will be able to fathom it throughout all eternity." (Diary of Saint Faustina, 699)
The devotion was celebrated unofficially in many places for some years. On April 30, 2000 (Divine Mercy Sunday of that year), Pope John Paul II canonized St. Faustina and designated the Sunday after Easter as Divine Mercy Sunday in the General Roman Calendar, with effect from the following year. He also decreed a plenary indulgence associated with this devotion. Pope John Paul II said he felt a closeness to St. Faustina when he was writing Dives in Misericordia. He died during the vigil of the Divine Mercy Sunday in 2005.
Sister Faustina was canonized a saint on April 30, 2000 Saint Faustina was born Helena Kowalska in the village of Glogowiec west of Lodz, Poland, on August 25, 1905. She was the third of ten children. When she was almost twenty, she entered the Congregation of the Sisters of Our Lady of Mercy, whose members devote themselves to the care and education of troubled young women. The following year she received her religious habit and was given the name Sister Maria Faustina, to which she added "of the Most Blessed Sacrament," as was permitted by her Congregation's custom. In the 1930s, Sister Faustina received from the Lord a message of mercy that she was told to spread throughout the world. She was asked to become the apostle and secretary of God's mercy, a model of how to be merciful to others, and an instrument for reemphasizing God's plan of mercy for the world.
The message of mercy that Sister Faustina received is now being spread throughout the world; she has been recognized by the Church as a "Saint"; and her diary, Divine Mercy in My Soul, has become the handbook for devotion to The Divine Mercy. She would not have been surprised, for she had been told that the message of God's mercy would spread through her writings for the great benefit of souls.
Through Saint Faustina, any person can leatn special ways to live out the response to Jesus’ mercy–one of which is the Chaplet of Divine Mercy, as both a novena and a prayer for the three o'clock hour–the hour of His death.
The Chaplet of the Divine Mercy will be recited at St Sebastian this Sunday, April 19 at 3:00 PM. The Chaplet of Mercy is recited using ordinary rosary beads of five decades. The Chaplet is preceded by two opening prayers from the Diary of Saint Faustina and followed by a closing prayer. For a complete understanding of Chaplet you can consult http://www.thedivinemercy.org/