“… 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 [Note: within a reasonable time before the Feast is sufficient; one must be in the state of grace to receive these special graces promised by Our Lord], and receive Holy Communion [on Divine Mercy Sunday] shall obtain complete forgiveness of sins and punishment.
On that day all the divine floodgates through which graces 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. …
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.”
— From the Diary of St. Faustina, Divine Mercy in My Soul, #699.
Note from Fr. Ben: It seems that this is essentially a plenary indulgence, which is the complete remission of all temporal punishment due to sin (which means all the stain/effects of sin in us that remains after the sins have been forgiven). What makes this different from other plenary indulgences is that the conditions are easier to fulfill. With other plenary indulgences, there is an indulgenced “work” such as a rosary in the presence of the Blessed Sacrament, or 15 minutes of Scripture reading, or some other special work like making a pilgrimage; and then we have to have Confession, Mass and Holy Communion, prayers for the intentions of the Holy Father, and detachment from our sins. There is no other indulgenced work required for Divine Mercy Sunday. I still recommend that we should pray for the Holy Father’s intentions, and we would be foolish if we think that Jesus will remit all stain/punishment due to sin if we are still clinging to our sins, whether they are mortal or venial. Maybe one of these “extraordinary graces” is that the Lord gives us extra help to let go of all our attachments to sin — but we still need to let go of our sins, to no longer hold onto our lust, or gluttony, or avarice, or pride, or anger, or any other sin that we seem to refuse to let go of in our daily lives.
May you have a most blessed, holy, and grace-filled Divine Mercy Sunday!