In the traditional Missale Romanum, it is referred to as “Dominica in albis octava Paschae” -- Sunday in White Within the Paschal Octave, when the robes of the neophytes are removed eight days after their initiation into the Sacraments during the Paschal Vigil. In the traditional Roman calendar, it was officially known as “The Octave Day of Easter” or more colloquially as “Low Sunday.” It was also popularly known as “Quasimodo Sunday” (my personal favorite, hence the title), after the first words of the Entrance Antiphon, or Introit: “Quasi modo geniti infantes, alleluia ...” (“Like newborn infants, alleluia ...”) In the Eastern churches, it is known as “Thomas Sunday” as the same gospel is read, that of our Lord showing himself to the doubting apostle Thomas.
Since 2000, by decree of the late Pope John Paul II, it is also known in the universal Roman calendar as Divine Mercy Sunday, "the culmination of the novena to the Divine Mercy of Jesus, a devotion given to St Faustina (Mary Faustina Kowalska) and is based upon an entry in her diary stating that anyone who participates in the Mass and receives the sacraments of Confession and the Eucharist on this day is assured by Jesus of full remission of their sins." (from Wikipedia)
(I already thought Confession did that anyway. This is what I get for using Wikipedia for the short version.)
This brings up an issue which has concerned traditional Catholics in recent years, one that is presented in a 2010 issue of New Oxford Review by Robert Allard: "Is Divine Mercy Sunday Liturgically Correct?"
It is interesting to note that in the Tridentine Latin Mass, the extraordinary form of the Roman Rite, the epistle reading, 1 John 5:4-10, includes the mention of the blood and water as portrayed in the Divine Mercy image, not just once but three times each. This is important to note because the Feast of Mercy was established for the entire Church universal, not just for the ordinary form of the Mass.
There's also that part about Our Lord breathing on the apostles, giving them the power of the Holy Spirit to forgive sins. There's a bit of mercy for the rest of us right there.
Such remembrances need to be harmonized with the liturgical season if they are to serve the faithful. This requires sufficient deference to the history of salvation as played out during the year, beginning with the incarnation, and on into the life, passion, death, and resurrection of our Lord, culminating in his ascension into Glory, and the establishment of His Church on Earth through the work of the Holy Spirit. That said, there is an aspect of this devotion that may appear problematic, one that has less to do with the Feast itself, than with the novena which precedes it, one that begins on Holy Thursday, and extends throughout the Week of Easter.
Q. My pastor will allow us to pray the Divine Mercy Novena, but not on Good Friday or Holy Saturday. He says it interferes with the Holy Triduum, which are the holiest days of the year.
A. The Paschal Triduum (Holy Thursday, Good Friday, and Holy Saturday) ushers in Easter Sunday and constitutes the most holy period of the Church year. The Divine Mercy Novena does not supersede the Triduum, but extends the Solemn General Intercessions of the Good Friday observance of Our Lord's Passion and Death throughout the whole octave of Easter, building up to the day of thanksgiving for Our Lord's Divine Mercy.
The problem with this response is that it belies the specific character of the Paschal Feast itself, and by extension, the octave which follows it.
For two millennia, the Easter season, particularly the Octave, has been devoted to the celebration of the resurrection. In the Eastern churches, where rules of fasting and abstinence have retained their traditional severity, the requirement to abstain from meat does not apply on the Friday of this octave, such is the extension of the occasion. The Fathers of the Church have told us, we have commemorated the fast, therefore let us celebrate the feast. Yet the greater part of the novena is devoted to chanting thus: "For the sake of His sorrowful Passion, have mercy on us and on the whole world." Granted, at every Mass offered on any given day, we remember the passion, death, and resurrection of Christ. But that comparison ends in the context of the liturgical year, the purpose of which is to shed a spotlight on a particular aspect of salvation history. There is sufficient reason to doubt that the emphasis made by this novena, in light of the timing, sheds that spotlight appropriately, even if we reduce it to a mere devotion (as opposed to the official prayer of the Church through her liturgical life).
If we read the history of the development of this Feast that is the Sunday within the Octave of Easter, if we understand what the readings and the orations are trying to tell us, we might consider the possibility that Our Lord was telling Sister Faustina something of Himself, which He has been trying to say to His Bride, our Mother the Church, all along. That said, She has long admonished us to be prudent with respect to the messages of private revelations. (See the Catechism of the Catholic Church, 65-67). And while accepting the judgment of the Apostolic See in this matter, we may long for a further study of this devotion in relation to the whole of the liturgical year, as discussions of a "reform of the reform" of our sacred worship continue in earnest.
After all, even if the novena is not "liturgy" in the official sense, its use in parishes during the octave of the resurrection is enough to give pause, in light of the "big picture."
We have commemorated the fast, therefore let us celebrate the feast.
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To learn more about the devotion to the Divine Mercy, visit the website of the Apostles of Divine Mercy at DivineMercySunday.com, or that of the Marians of the Immaculate Conception at TheDivineMercy.org. For a guide to praying the Chaplet of the Divine Mercy, go to the appropriate page at EWTN.com.