The Divine Mercy Image
Maria Faustina Kowalska, now known as Saint Faustina, was a nun, mystic and visionary in Poland at the beginning of the 20th century.
On February 22, 1931 she reports in her diary of a vision of Christ with a command:
“In the evening, when I was in my cell, I saw the Lord Jesus clothed in a white garment. One hand raised in the gesture of blessing, the other was touching the garment at the breast. From beneath the garment, slightly drawn aside at the breast, there were emanating two large rays, one red, the other pale. In silence I kept my gaze fixed on the Lord; my soul was struck with awe, but also with great joy. After a while, Jesus said to me, Paint an image according to the pattern you see, with the signature: Jesus, I trust in You. I desire that this image be venerated, first in your chapel, and [then] throughout the world. I promise that the soul that will venerate this image will not perish. I also promise victory over enemies already here on earth, especially at the hour of death. I myself will defend it as My own glory”. 
In the image described by Saint Faustina, Jesus was depicted with his right hand raised in blessing to mankind, as if saying: “Peace be with you”, these are words we hear in the liturgy on the Sunday after Easter. On this Sunday St. John’s gospel relates the resurrected Jesus appearance in the room of the last supper and of the institution of the sacrament of reconciliation. In the painting we see the rays of blood and water flowing from the veiled pierced heart of Jesus, and the wounds on his hands and feet giving witness to the events of Good Friday. The picture of Divine Mercy unites the two gospel events, which is the greatest witness of the merciful love of God for all his people. 
It is through the visions of Christ given to St. Faustina that became the institution of the celebration of Divine Mercy Sunday on the Sunday following Easter.
From the Divine Liturgy of St John Chrysostom (“Gospodi Pomiluj” = “Lord Have Mercy”):