The Divine Mercy devotion is based on the writings of Saint Faustina Kowalska, a Polish nun who wrote a diary of about 600 pages recording revelations she received about God's mercy. The devotion was actively promoted by Pope John Paul II who canonized Faustina on April 30, 2000, and declared the Sunday after Easter as Divine Mercy Sunday.
Jesus told St. Faustina: "Humanity will not find peace until it turns trustfully to Divine Mercy." The message of mercy is that God loves us — all of us, regardless of our faults. He wants us to recognize that His mercy is greater than our sins, so that we will call upon Him with trust, receive His mercy, and let it flow through us to others.
"Let no soul fear to draw near to Me, even though its sins be as scarlet."— Words of Jesus to St. Faustina