In bhagavad gita God says that I am the highest of the high. I am never born nor do I die. I am absolute Knowledge, I am absolute purity, I am eternal light.  I am Infinite. I am omnipotent. I am an energy in the form of light. A very subtle point of light.    

 Now why just a point of light? 

God further explains that a point is infinite, has no dimensions, no measurements. Point is indestructible and so am I.

Point of Light personifies purity and divinity. Light is the reminder of brightness taking away the darkness. God is light because he is the definition of purity, divinity. He is absolute in all his qualities. He does not have even a speck of impurity in him. He is the paragon of absoluteness. In religion also it is accepted that God takes away the darkness from every human soul and enlightens the human beings so he is the ultimate point of light. As I mentioned his name is Shiv -Shiv also means point of light. Therefore God reveals that he is a tiny dot in the form of light.