What do the rays of light shining from the Heart of Jesus represent?

In her Diary, St. Faustina said,

When on one occasion my confessor told me to ask the Lord Jesus the meaning of the two rays in the image, I answered, “Very well, I will ask the Lord.”
During prayer I heard these words within me: The two rays denote Blood and Water. The pale ray stands for the water that 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)