‘And I saw no Temple in it, for the Lord God, the Almighty, and the Lamb are its Temple. And the city has no need of the sun nor of the moon to shine on it, for the glory of God did lighten it and its lamp is the Lamb.'
No temple is needed for the Lord God walks within it. He and the Lamb are its Temple, i.e. men worship directly and personally face to face. It has no need of any light other than the light of God and the Lamb (compare Isaiah 60:19). The whole place is filled with Their glory.
‘No sun and moon.' This would come as a shock to those who worshipped the sun and the moon. The idolatrous ideas of men are finished with. Nor will God's people ever again have to call on light other than the perfect light of God. Compare Isaiah 60:19. This is the final fulfilment of what the prophets promised.