Feast of Divine Mercy
Jesus said to Sr. Faustina: Souls perish in spite of My bitter Passion. I am giving them the last hope of salvation; that is, the Feast of My Mercy. If they will not adore My mercy, they will perish for all eternity (Diary 965).
The Feast of Divine Mercy allows us in particular to penetrate the unfathomable mystery of God's merciful love towards each human being and thereby take heart and trust in his immeasurable goodness. A novena which begins on Good Friday, consisting of the Divine Mercy Chaplet, is a preparation to celebrate the Feast of Divine Mercy. Jesus said to St. Faustina about his desire to establish the Feast for the first time in Płock in 1931:
I desire – He said to Sr. Faustina – that the Feast of Mercy be a refuge and shelter for all souls, and especially for poor sinners. On that day the very depths of My tender mercy are open. I pour out a whole ocean of graces upon those souls who approach the Fount of My Mercy. The soul that will go to Confession and receive Holy Communion shall obtain complete forgiveness of sins and punishment (Diary 699).
The greatest and unimaginable grace of the Divine Mercy Sunday has been directly associated with the Holy Communion received on this day. This grace lies in the complete forgiveness of punishment and sins. Confession does not need to take place on this day, it can be done earlier. This is important that one's soul is pure, without any attachment to any sins.
The Holy Father John Paul II on the day of Sr. Faustina Kowalska's canonization, i.e. 30th April 2000, established the Feast of Divine Mercy for the whole Church.