During the course of Jesus’ revelations to Saint Faustina on the Divine Mercy He asked on numerous occasions that a feast day be dedicated to the Divine Mercy and that this feast be celebrated on the Sunday after Easter.
In a decree dated 23 May 2000, the Congregation for Divine Worship and the Discipline of the Sacraments stated that “throughout the world the Second Sunday of Easter will receive the name Divine Mercy Sunday, a perennial invitation to the Christian world to face, with confidence in divine benevolence, the difficulties and trials that mankind will experience in the years to come.”
Concerning the Feast of Mercy Jesus said:
Whoever approaches the Fountain of Life on this day will be granted complete forgiveness of sins and punishment. (Diary 300)
I want the image solemnly blessed on the first Sunday after Easter, and I want it to be venerated publicly so that every soul may know about it. (Diary 341)
This Feast emerged from the very depths of My mercy, and it is confirmed in the vast depths of my tender mercies. (Diary 420)
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.* [our emphasis] 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 I 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)