God is light and in Him is no darkness at all: We must begin our understanding of God here. John declares this on the simple understanding that God Himself is light; and light by definition has no darkness at all in it; for there to be darkness, there must be an absence of light.
i. A good definition of God is, "God is the only infinite, eternal, and unchangeable spirit, the perfect being in whom all things begin, and continue, and end." Another way of saying that God is perfect is to say that God is light.
ii. "LIGHT is the purest, the most subtle, the most useful, and the most diffusive of all God's creatures; it is, therefore, a very proper emblem of the purity, perfection, and goodness of the Divine nature." (Clarke)
iii. "There are spots in the sun, great tracts of blackness on its radiant disc; but in God is unmingled, perfect purity." (Maclaren)