After his resurrection, Jesus appeared to his apostles, but Thomas wasn't among them. So when they told him about it he didn't believe them saying that he will only believe it if he gets to touch Jesus's wounds.
So Jesus appears before him and makes him touch his wounds to show him that he has indeed returned from the dead. The painting is about that.
It just works, but i have to admit it gave me some headaches trying to explore the avaliable patches. Not all patches work and you might have issues after applying and compiling