A rather new addition to the calendar originated from a vision a Polish nun had of Jesus
It is not very often in the Church when a new liturgical feast is established that is not associated with a saint’s feast day. It happens very rarely and is never done lightly. However, in 2000, Saint John Paul II canonized the Polish religious mystic Faustina Kowalska and during his homily officially renamed the Second Sunday of Easter “Divine Mercy Sunday.”
John Paul II did this to endorse Faustina’s visions as well as to put more emphasis on Divine Mercy in the 21st century. He explained during his homily, “Divine Mercy reaches human beings through the heart of Christ crucified: ‘My daughter, say that I am love and mercy personified,’ Jesus will ask Sr. Faustina (Diary, p. 374). Christ pours out this mercy on humanity though the sending of the Spirit who, in the Trinity, is the Person-Love. And is not mercy love’s ‘second name’ (cf. Dives in misericordia, n. 7), understood in its deepest and most tender aspect, in its ability to take upon itself the burden of any need and, especially, in its immense capacity for forgiveness? Today my joy is truly great in presenting the life and witness of Sr. Faustina Kowalska to the whole Church as a gift of God for our time … Jesus told Sr Faustina: ‘Humanity will not find peace until it turns trustfully to divine mercy’ (Diary, p. 132).”
The Polish pope then went on to proclaim, “It is important then that we accept the whole message that comes to us from the word of God on this Second Sunday of Easter, which from now on throughout the Church will be called ‘Divine Mercy Sunday.’”
Traditionally the Second Sunday of Easter was nicknamed Low Sunday, in contrast to the High Sunday of Easter. In the Middle Ages it was known as Quasimodo (“In the manner of”) Sunday, from the Latin words that began the Introit: “As newborn babes desire milk” (1 Peter 2:2). It was on this day that Victor Hugo’s fictional hunchback infant was abandoned on the steps of Notre Dame Cathedral, and given the name Quasimodo — which can also mean “half-formed.” The last day of the Easter Octave, this Sunday has always featured the Gospel of “Doubting Thomas.” This particular Gospel is often said to remind us of the need to enter into Jesus’ heart to be washed clean through his mercy.
Jesus requested that this Second Sunday of Easter be named “Divine Mercy Sunday” in a vision to Saint Faustina that she wrote down in her Diary.
On one occasion, I heard these words: My daughter, tell the whole world about My Inconceivable mercy. I desire that the Feast of Mercy be a refuge and shelter for all souls, and especially for poor sinners. 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. Everything that exists has come forth from the very depths of My most tender mercy. Every soul in its relation to Me will contemplate My love and mercy throughout eternity. The Feast of Mercy emerged from My very depths of tenderness. It is My desire that it be solemnly celebrated on the first Sunday after Easter. Mankind will not have peace until it turns to the Fount of My Mercy. (Diary 699)
Yes, the first Sunday after Easter is the Feast of Mercy, but there must also be deeds of mercy, which are to arise out of love for Me. You are to show mercy to our neighbors always and everywhere. You must not shrink from this or try to absolve yourself from it. (Diary 742)
This year, the Second Sunday of Easter falls on April 23, and so it is this day when we also celebrate Divine Mercy Sunday.