Albert Barnes Commentary Revelation 21:23

"And the city hath no need of the sun, neither of the moon, to shine upon it: for the glory of God did lighten it, and the lamp thereof [is] the Lamb." — Revelation 21:23 (ASV)

And the city had no need of the sun, neither of the moon, to shine in it. This imagery seems to be derived from Isaiah 60:19-20. See Barnes on Isaiah 60:19. See Barnes on Isaiah 60:20.

No language could give a more striking or beautiful representation of the heavenly state than that which is here employed.

For the glory of God did lighten it. It was illumined by the visible splendor of his glory. See Barnes on Revelation 21:11.

That splendor supplied the place of the sun and the moon.

And the Lamb is the light of it. He is the Son of God, the Messiah. See Barnes on Revelation 5:6 and Isaiah 60:19.

(Compare John 1:4, regarding the light).