Ganaka Vaideha said: 'When the sun has set, O Yagnavalkya, what is then the light of man?' Yagnavalkya replied: 'The moon indeed is his light; for, having the moon alone for his light, man sits, moves about, does his work, and returns.' Ganaka Vaideha said: 'So indeed it is, O Yagnavalkya.'

In plain words: Janaka asks what gives a person light after the sun has set. Yagnavalkya says the moon, because by its light we can still sit, move, work and come home. The king agrees.