I STARTED DESCRIBING DIVINE MERCY IN MY LAST BLOG. THIS CONTINUES:
The reason this Sunday is celebrated as Divine Mercy Sunday is because this is the Sunday that the Gospel according to St. John about the risen Christ appearing in the Upper Room and about the institution of the Sacrament of Penance (Jn 20″19-29) Consequently, this image represents the Savior risen from the dead who brings peace to people by means of the forgiveness of sins at the price of His passion and death on the cross.
In 1931 in Plock, Poland our Lord communicated His will regarding the painting of the Image of Divine Mercy: “I desire that there be a Feast of Mercy. I want this image, which you will paint with a brush, to be solemnly blessed on the first Sunday after Easter; that Sunday is to be the Feast of Mercy” (Saint Faustina’s diary, 49). I will try to post a copy of the photo when I can.
The rays of blood and water that flow from the Heart that was pierced by a spear (not visible on the image) and the scars caused by the wounds of crucifixion call to mind the events of Good Friday (Jn 19:17-18; 33-37) The pay ray stands for the Blood which makes souls righteous. The red ray stands for the Blood which is the life of souls…Happy is the one who will dwell in their shelter: (Diary, 299). The Sacraments of Baptism and Penance purify the soul, and the Eucharist most abundantly nourishes it. Thus, the two rays signify the Holy Sacraments and all the graces of the Holy Spirit, whose biblical symbol is water, as well as the New Covenant of God with men in the Blood of Christ.
This is briefly why we celebrate Divine Mercy Sunday, say the Divine Mercy Chaplet and the Novena. You should be able to get more information on: http://www.catholic.com