… Jesus wanted this feast to be established is that He wanted to “throw a lifeline,” so to speak, to souls who are perishing, souls who are drowning in sin and despair. That lifeline is this Feast, with all the tremendous promises of graces and benefits which Jesus attached to it. As He said to St. Faustina, He wanted to make this Feast day a special “refuge and shelter” for the “consolation” of souls. In Diary entry 1517, Jesus said: “the Feast of My Mercy has issued forth from My very depths for the consolation of the whole world.” In short, Jesus gave us this Feast as both a comfort and a lifeline for souls.
Second, “when” is this Feast to be celebrated? The answer was given directly to St. Faustina on numerous occasions. For example, in Diary entry 299, Jesus said to her: “I desire that the First Sunday after Easter be the Feast of Mercy.” Today that Sunday is called in the Roman Missal “The Second Sunday of Easter, or Divine Mercy Sunday.”
Third, in order to discover “who” is invited to this great Feast, and what kind of spiritual “banquet” our Lord wants to spread for us on that day, we need to consult Diary entry 699, in which Jesus spells out in detail the meaning of this feast day, and the comforting promises He attached to it. Jesus said to St. Faustina:
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.