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

In plain words: King Janaka (Ganaka Vaideha) asks the sage Yajnavalkya what lights a person's way once both the sun and the moon have set. Yajnavalkya answers that fire is then the light that lets a person sit, move about, work and come home.