Divine Mercy Sunday

"The liturgical Fest of The Divine Mercy . . . falls on the Sunday after Easter, which is the Octave Day of Easter. As we know from The Apostolic Constitutions, and the writings of St. Augustine and St. Gregory Nazianzen, this day was always kept as a special feast by the ancient Church. It was known by them as "the Sunday in White (Dominica in Albis) because those newly baptized at Easter wore their white baptismal robes up through that day. St. Augustine called the whole octave "the days of mercy and pardon," and the Sunday "the compendium of the days of mercy." Now revived as "Mercy Sunday," this feast enables the Church to celebrate the merciful love of Jesus Christ that flows from His Sacred Heart, and that lies behind all the acts He has undertaken for our salvation. As Pope John Paul II said in his Regina Caeli address on Mercy Sunday in 1995, "the whole Octave of Easter is like a single day," and the Octave Sunday is meant to be the day of "thanksgiving for the goodness God has shown man in the whole Easter mystery."

The above quote comes from Jesus, Mercy, Incarnate by
Dr. Stackpole, the director of the John Paul II Institute of Divine Mercy in Stockbridge, Massachusetts, and one of my theology professors.