“We may have been forgiven for our sins sacramentally confessed, but we will have to pay for them on earth and, if death strikes too soon, in Purgatory. But this coming Sunday, we have the chance to scrap such debt. It will be Divine Mercy Sunday that, as decreed by the late St. Pope John Paul II, gives us the chance to avail ourselves of Plenary Indulgence- a total remission of purgation owed for sins.
“There are two things that can be had this Divine Mercy Sunday: the "special graces" promised by Our Lord Jesus, and the Plenary Indulgence offered by the Church for special devotions to the Divine Mercy
“To receive special graces that our Lord promised for Divine Mercy Sunday, the only condition is to receive Holy Communion worthily (or the Vigil celebration) by making a good Confession beforehand and staying in the state of grace and trusting in His Divine Mercy.
“On the other hand, Plenary Indulgence granted by the Church involves the fulfilment of conditions, including prayer for the Holy Father's intentions, Confession and Holy Eucharist, and the carrying out of the special indulgenced work such as participating in public devotions to the Divine Mercy on Divine Mercy Sunday itself.”
Source: Cervantes, sunstar.com.ph