Divine Mercy Sunday is a Roman Catholic solemnity celebrated on the Sunday after Easter, the Octave of Easter. It is originally based on the Catholic devotion to the Divine Mercy that Saint Faustina Kowalska reported as part of her encounter with Jesus, and is associated with special promises from Jesus and indulgences issued by the Church.
This feast of Divine Mercy, as recorded in the diary of Saint Faustina, receives from Jesus himself the biggest promises of Grace related to the Devotion of Divine Mercy. In specific Jesus states that the soul that goes to Sacramental Confession (the confession may take place some days before), and receive Holy Eucharistic Communion on that day, shall obtain the total forgiveness of all sins and punishment. Additionally, the Roman Catholic Church grants a plenary indulgence (observing the usual rules) with the recitation of some simple prayers.