And the city had no need of the sun, neither of the moon, to shine in it: for the glory of God did lighten it, and the Lamb is the light thereof.
God’s revelation to man begins with God’s light (“Let there be light” - Gen. 1:3), and here in Revelation the Glory of God illuminates the heavenly city of God. There is literally no need for the sun. If the sun and moon did shine, they would give no added light in the presence of the Glory of God. In the Lamb light is concentrated, and from Him it is everywhere diffused.