The Divine Mercy Novena begins on Good Friday and ​is completed on the Sunday after Easter.

THE HISTORY 
Jesus began appearing to St. Faustina Kowalska, a Polish nun, in 1931. The message and devotion to Jesus as The Divine Mercy is based on her published diary recording the revelations she received from Jesus. St. Faustina died in 1938, at 33 years old, and was canonized by St. John Paul II in 2000. 

THE PROMISE 
Our Lord Jesus said, "The soul that will go to Confession and receive Holy Communion shall obtain complete for- giveness of sins and punishment. On that day all the divine floodgates throughout which graces flow are opened. Let no soul fear to draw near to Me, even though its sins be as scarlet... Mankind will not have peace until it turns to the Fount of My Mercy." 
- Saint Faustina, Diary, 699 

WHY IS THIS PROMISE FROM JESUS 
SO WONDERFUL AND MERCIFUL?

TEMPORAL PUNISHMENT AND SUFFERING 
The Catholic Church teaches that sin has two consequences, or punishments. (CCC 1472). The first is eternal punish- ment in which the soul loses heaven and is confined to an eternity in Hell. This punishment is remitted through the forgiveness of sins. The second is temporal punishment, in which a person must expiate, or make reparation for his sins. This temporal punishment remains even after sin is forgiven. This temporal punishment is known as Purgatory. 
So, Jesus's amazing promise to St. Faustina amounts to offering all mankind the graces of a COMPLETE PARDON; an opportunity to have all temporal punishment, time in Purgatory, that which would be necessary before entrance into Heaven, completely removed! 

TO OBSERVE DIVINE MERCY SUNDAY 
Sincerely repent of all of your sins. Place your complete trust in Jesus. Go to Confession, the Church permits up to 20 days before the Feast. Receive Holy Communion on Divine Mercy Sunday. Venerate the image, such as a prayer before it, "Merciful Jesus, I trust in You!" Be merciful to others, through actions, words, and prayers. 

THE IMAGE
"I desire that this image be venerated throughout the world. I promise that the soul that will venerate this image will not perish. I promise victory over its enemies, already here on earth, and especially at the hour of death...I Myself will defend it as My own glory."
 
THE CHAPLET
"Pray unceasingly the Chaplet that I have taught you. Whoever will recite it will receive great mercy at the hour of death. Priests will recommend it to sinners as their last hope of salvation." 

THE CONVERSION PRAYER
"If you say this prayer, with a contrite heart and with faith, 
on behalf of some sinner, I will give that soul the grace of conversion: 
'O Blood and Water that gushed forth from the heart of Jesus, as a fount of mercy for us, I trust in You.' 
- Diary 186, 187 

Know, My daughter, that this prayer is always heard and answered." 
- Diary 1397 

SPREAD OF THE DEVOTION
"Do whatever is within your power to spread devotion to my mercy. I will make up for what you lack." 

Our Lord's promises attached to the praying of the Chaplet of Divine Mercy as revealed to Saint Faustina Kowalska 

1. "I promise that the soul that will venerate this image (of Divine Mercy) will not perish. I also promise victory over (its) enemies already here on earth, especially at the hour of death. I Myself will defend it as My own glory." 

2. "The two rays denote Blood and Water...These two rays issued from the very depths of My tender mercy when My agonized Heart was opened by a lance on the Cross. These rays shield souls from the wrath of My Father...I desire that the first Sunday after Easter be the Feast of Mercy...whoever approaches the Fount of Life on this day will be granted complete remission of sins and punishment. Mankind will not have peace until it turns with trust to My mercy." 

3. "I desire that the Feast of Mercy...be solemnly celebrated on the first Sunday after Easter... The soul that will go to Confession and receive Holy Communion (in a state of grace on this day) shall obtain complete forgiveness of sins and punishment." 

4. "Whoever will recite it will receive great mercy at the hour of death." 

5. "Priests will recommend it to sinners as their last hope of salvation. Even if there were a sinner most hardened, if he were to recite this chaplet only once, he would receive grace from My infinite mercy...I desire to grant unimaginable graces to those souls who trust in My mercy.” 

6. "The souls that say this chaplet will be embraced by My mercy during their lifetime and especially at the hour of their death." 

7. "Souls who spread the honor of My mercy...at the hour of death I will not be a Judge for them, but the Merciful Savior." 

8. "The prayer most pleasing to Me is prayer for the conversion for sinners. Know, my daughter, that this prayer is always heard and answered."
 
9. "My mercy is greater than your sins and those of the entire world." 

10. "To priests who proclaim and extol My mercy, I will give wondrous power; I will anoint their words and touch the hearts of those to whom they will speak." 

11. "Through this chaplet you will obtain everything, if what you ask for is compatible with My will.' 

12. "When hardened sinners say it, I will fill their souls with peace, and the hour of their death will be a happy one." 

13. "When they say this chaplet in the presence of the dying, I will stand between My Father and the dying person, not as a just Judge but as a merciful Savior." 

14. "At three o'clock, implore My mercy, especially for sinners; and, if only for a brief moment, immerse yourself in My Passion, particularly in My abandonment at the moment of agony...I will refuse nothing to the soul that makes a request of Me in virtue of My Passion." 

How to pray the chaplet of Divine Mercy

Download the Divine Mercy Novena