This message was banned in the church for 20 years and then when John Paul II became the Holy Father in 1978, one of the first things he did was to un-ban and encourage the devotion. He also established the Sunday after Easter as Divine Mercy Sunday.

On Divine Mercy Sunday you can receive the Divine Mercy Grace (a Plenary Indulgence) which means it restores you to the way you were after Baptism - sinfree.  In order to receive this Divine Mercy Grace (which was established by John Paul II) you must go to confession within 20 days of Divine Mercy Sunday, receive Communion on that Sunday with the intent of receiving the Divine Mercy Grace and then pray for the Holy Father.

St Faustina, a deep mystic sister who lived in the first part of the 20th century, is admittedly not easy to understand and some feel the Divine Mercy message was banned due to her being so difficult to understand.

But looking at the devotion (which now is encouraged in our church) a second time, reveals that regardless of whether we understand the humble messenger, Divine Mercy seems to be a message just for these times when trust comes so hard to all of us.

We are constantly hit by "spin" (or as Orwell said - newspeak) in our world today.  In other words, most of what we hear on a daily basis, are lies.  And also, people tend to be distrustful of each other. Opening up to another person is difficult and becomes more difficult when we have opened up and then, the other person becomes flakey and hurts our feelings.

How then can we trust Jesus the way we must trust Him when it's so difficult to trust everyone we see around us.  Every time someone asked Jesus one of the hard questions like What is heaven like or how does salvation work or what does God look like, He became what might be perceived as evasive and told us to just trust Him.  This is thought to be because there is no way we can understand the answers to those questions. It would be like explaining the birthing process to a 1 year old child.  We cannot do this and must obtain the child's trust through our actions of love we show to the child.

We must trust Jesus by His Actions, by the Love He showed for each one of us when He totally subjected Himself to our abuse and willingly, died on the cross, giving his life as the Ultimate Act of Love.  We must believe in Heaven by seeing the actions of Jesus when He resurrected and told us that He was going to prepare a place for us to live in eternal happiness. 

The message of Divine Mercy elaborates on how much Jesus wants to give to us if we can manage to open our hearts to Him:

The graces of My mercy, Jesus told Sister Faustina, are drawn by means of one vessel only, and that is trust. The more a souls trusts, the more it will receive. Souls that trust boundlessly are a great comfort to Me, because I pour all the treasures of My graces into them. I rejoice that they ask for much, because it is my desire to give them much, very much. The soul that will trust in My mercy is most fortunate, because I Myself will take care of it. No soul that has called upon My mercy has been disappointed or brought to shame. I delight particularly in a soul which has placed its trust in My goodness

Were a soul like a decaying corpse so that from a human standpoint, there would be no hope of restoration and and everything would already be lost, it is not so with God. The miracle of Divine Mercy restores that soul in full. Oh how miserable are those who do not take advantage of the miracle of God’s mercy!

More information:

http://www.divinemercysunday.com/

Dives in misericordia: text - IntraText SC

Saint Faustina