God is omniscient, that is, he is aware of, sees, and knows all things, because he is wisdom itself and light itself. Wisdom itself is aware of all things.
Light itself sees all things.
We showed above (Section 37) that God is wisdom itself. He is light itself because he is the sun of the angelic heaven that enlightens the intellect of all, both angels and people. As our eye is illuminated by the light of the physical sun, so our intellect is illuminated by the light of the spiritual sun—not only illuminated, but also filled with intelligence (depending on how much we love receiving it), since spiritual light is essentially wisdom.
This is why it says in David that God dwells in inaccessible light [Psalms 104:2; see also 1 Timothy 6:16]; and why it says in the Book of Revelation that in the New Jerusalem they do not need lamps because the Lord God enlightens them [Revelation 21:23]; and why it says in John that the Word that was with God and was God is the light that enlightens everyone who comes into the world [John 1:1, 9]. The “Word” in this last reference means divine wisdom. This is why the more wisdom angels have, the brighter a light they are in; and why when “light” is mentioned in the Word it means wisdom.
from True Christianity, Section 59