From How to Celebrate Divine Mercy Sunday
During the Mass of canonization of St. Faustina on April 30, 2000, the year of the Great Jubilee, Pope John Paul II proclaimed: "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." The readings on that Sunday are always about mercy, trust and the forgiveness of sins.
By the words "the whole message," the Holy Father was referring to the strict connection between the "Easter Mystery of the Redemption" -- the suffering, death, burial, resurrection, and ascension of Christ, followed by the sending of the Holy Spirit -- and this Feast of Divine Mercy, on the Octave Day of Easter. This feast adds so much more meaning to the Easter celebrations. It was Jesus, Himself who asked for it to be celebrated on this particular Sunday following Easter.
There has been much confusion as to how this feast is to be celebrated. To know how to celebrate the Feast, one must only look at the two decrees that were issued by the Holy See and the words of Our Lord in the diary of St. Faustina, which the Church has accepted, as reliable and worthy of belief.
The first decree which established the Feast states that the normal readings for that Sunday are always to be used. They are already perfect as they are and reflect what the Image of Divine Mercy portrays.
The second decree is for the plenary indulgence for Divine Mercy Sunday that was issued on June 29, 2002. This decree also states what the specific duties of Priests are to be: "Inform the parishioners, hear confessions, and lead the prayers. The indulgence decree also asks Priests to gently encourage the Faithful to practice works of charity or mercy as often as they can, following the example of Christ."
The words of Our Lord in the diary are very clear, He said, "I want the image to be solemnly blessed on the first Sunday after Easter, and I want it to be venerated publicly so that every soul may know about it. By means of the Image I shall be granting many graces to souls; so let every soul have access to it." (Diary 341, 570) The Image should be placed in the church so that everyone can see it, perhaps in the sanctuary area and at all the masses on that day so that everyone may venerate and know about it.
Our Lord also said, "I desire that priests proclaim this great mercy of Mine towards souls of sinners. Tell My priests that hardened sinners will repent on hearing their words when they speak about My unfathomable mercy, about the compassion I have for them in My Heart. To priests who proclaim and extol My mercy, I will give wondrous power; I will anoint their words and touch the hearts of those to whom they will speak." (Diary, 50, 1521) Easter Sunday is the best time to proclaim God’s mercy.
Our Lord Jesus said, "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 graces flow are opened. Let no soul fear to draw near to Me, even though its sins be as scarlet.... Mankind will not have peace until it turns to the Fount of My Mercy." (699) The plenary indulgence that was issued for Divine Mercy Sunday does not change the promises of Our Lord. Rather it provides the Church's highest mark of approval and endorsement and gives souls more time to go to Confession.
Our Lord also said, "The first Sunday after Easter is the Feast of Mercy, but there must also be acts of mercy....I demand from you deeds of mercy, which are to arise out of love for Me." (Diary, 742) It is clear that Our Lord wants mercy to be shown to others and this can be done by telling everyone about the special promise of the total forgiveness of sins and punishment that He has graciously given to us.
In the Holy Father's homilies, he often refers to the words of Our Lord that are found in the diary. In his homily on Divine Mercy Sunday in 2001 in Rome he said, "It is the appropriate and incisive answer that God wanted to offer to the questions and expectations of human beings in our time, marked by terrible tragedies. Divine Mercy! This is the Easter gift that the Church receives from the risen Christ and offers to humanity.'' He often quotes Our Lord by starting with "Jesus said to St. Faustina." He spoke of the Image of The Divine Mercy saying "The two rays, according to what Jesus Himself told her, denote blood and water. The blood recalls the sacrifice of Golgotha and the mystery of the Eucharist: the water makes us think of Baptism and the Gift of the Holy Spirit."
So as we can see, the celebration of Divine Mercy Sunday is quite simple, in fact, outside of having an image of The Divine Mercy in the church to venerate, there really isn’t anything else to do on that day itself. It is Jesus Himself that does all the work on that day. Most of the energy should be focused on getting people to come back Church on Divine Mercy Sunday. Jesus will do the rest. All that we need to do is to tell everyone about the plenary indulgence and urge them to go to Confession. We cannot forget that Easter Sunday is the best time for us to talk about mercy, because the churches are so full.
The following "General remarks on Indulgences" from Gift of the Indulgence summarizes the usual conditions given in the Church's law (cf. Apostolic Penitentiary, Prot. N. 39/05/I):
1. This is how an indulgence is defined in the Code of Canon Law (can. 992) and in the Catechism of the Catholic Church (n. 1471): "An indulgence is a remission before God of the temporal punishment due to sins whose guilt has already been forgiven, which the faithful Christian who is duly disposed gains under certain prescribed conditions through the action of the Church which, as the minister of redemption, dispenses and applies with authority the treasury of the satisfactions of Christ and the saints".
2. In general, the gaining of indulgences requires certain prescribed conditions (below, nn. 3, 4), and the performance of certain prescribed works ..... [in this case, those granted for the Feast of Mercy]
3. To gain indulgences, whether plenary or partial, it is necessary that the faithful be in the state of grace at least at the time the indulgenced work is completed. [i.e. one must be a Catholic, not excommunicated or in schism.]
4. A plenary indulgence can be gained only once a day. In order to obtain it, the faithful must, in addition to being in the state of grace:
—have the interior disposition of complete detachment from sin, even venial sin;
—have sacramentally confessed their sins;
—receive the Holy Eucharist (it is certainly better to receive it while participating in Holy Mass, but for the indulgence only Holy Communion is required);
—pray for the intentions of the Supreme Pontiff.
5. It is appropriate, but not necessary, that the sacramental Confession and especially Holy Communion and the prayer for the Pope's intentions take place on the same day that the indulgenced work is performed; but it is sufficient that these sacred rites and prayers be carried out within several days (about 20) before or after the indulgenced act. Prayer for the Pope's intentions is left to the choice of the faithful, but an "Our Father" and a "Hail Mary" are suggested. One sacramental Confession suffices for several plenary indulgences, but a separate Holy Communion and a separate prayer for the Holy Father's intentions are required for each plenary indulgence.
6. For the sake of those legitimately impeded, confessors can commute both the work prescribed and the conditions required (except, obviously, detachment from even venial sin).
7. Indulgences can always be applied either to oneself or to the souls of the deceased, but they cannot be applied to other persons living on earth.