(Divine Mercy is one of those terms, that when you first hear it, it bounces our hard shell because it doesn't sound like anything that would apply to our lives. However, the more you learn about God's mercy, the more you realize it is a part of everyday life as much as breathing, but in an unseen way.
St. Faustina saw in many visions, the image of the Divine Mercy Jesus that we see painted today. She didn't like the painting that was done of the image and complained to Jesus that it wasn't as beautiful as the visions she saw. But in obedience, she accepted. I personally like the this icon representation or this version a little better than the original, but that's not the point of the image.
The point of the image is to remind us, like Jesus said in the revelations to St. Faustina, is that he is dying to pour his mercy upon us, if we would only accept it. The red rays symbolize
Jesus says it pains him when souls will not accept his mercy. How many times in day, do I refuse to accept God's mercy by my pride? too many to count. Yet, that is the cool thing about Divine Mercy. The bigger the sinner, the bigger the sin, the happier it makes Jesus to give His mercy! He wants to give us his love and mercy if we would only let him. That's the caveat.
In big ways and small ways, we hold on to our sins. We don't want to admit that we did something wrong.)
Here is a image of St. Faustina and the Dvine Mercy image.