Jesus commissioned St. Faustina to have a special image painted, an image that would reflect His Mercy and help spread the message of His great love. He wanted the world to know His mercy through this image and grants many specials graces through it.
"In the evening, when I was in my cell, I saw the Lord Jesus clothed in a white garment. One hand [was] 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." (Diary, 47)
"I am offering people a vessel with which they are to keep coming for graces to the fountain of mercy. That vessel is this image with the signature; 'Jesus, I trust in You.'" (Diary,327)
She was to have the image painted just as she saw Him, standing with His right hand raised in blessing, red and pale rays issuing from His heart, a gaze of Mercy in His eyes...
"During prayer I heard these words within me: The two rays denote Blood and Water. The pale ray stands for the Water which makes souls righteous. The red ray stands for the Blood which is the life of souls...
These two rays issued forth from the very depths of My tender mercy when My agonized Heart was opened by a lance on the Cross. (Diary,299)
"My gaze from this image is like My gaze from the cross." (Diary, 326)
Our Lord was very specific about how he wanted the image venerated...
"Tell the confessor that the Image is to be on view in the church and not within the enclosure in that convent. By means of this Image I shall be granting many graces to souls; so let every soul have access to it." (Diary, 570)
"I desire that this image be displayed in public on the first Sunday after Easter. That Sunday is the Feast of Mercy. Through the Word Incarnate I make known the bottomless depth of My mercy." (Diary, 88)
In His great Mercy, Jesus promises a great deal to those who venerate this image...
"I promise that the soul that will venerate this image 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." (Diary, 48)
"By means of this image I shall grant many graces to souls. It is to be a reminder of the demands of My mercy...." (Diary, 742)
"These rays shield souls from the wrath of My Father. Happy is the one who will dwell in their shelter, for the just hand of God shall not lay hold of him. I desire that the first Sunday after Easter be the Feast of Mercy." (Diary,299)
"When you say this prayer, with a contrite heart and with faith on behalf o f some sinner, I will give him the grace of conversion. This is the prayer:
'O Blood and Water, which gushed forth from the Heart of Jesus as a fount of Mercy for us, I trust in You'" (Diary, 186-7)
"Not in the beauty of the color, nor of the brush lies the greatness of this image, but in My grace." (Diary, 313)