And light in the Old Testament means life itself. This is not strange since we know from modern science that life came about from light and water. This confirms the story of Creation in the first pages of the Book of Genesis. God is light, meaning that God is life and the Giver of Life. Love does not exist by itself.
Love is creative.
It directs itself towards the other. For this reason God created free beings to give them His glory and share with Him the divine joy in the Trinity. The first created beings were angels. That's why angels, as St. Gregory calls them, are secondary lights. Angels are secondary lights because they draw their light and life from God, as the moon receives its light from the sun.