That Buddhi (understanding) which has the self for its object, is night to all beings, i.e., is obscure like night to all. But he, who has subdued the senses and is serene, is awake in respect of the self. The meaning is that he has the vision of the self. All beings are awake, i.e., are actively cognisant in respect of objects of the senses like sound. But such sense objects are like things enshrouded by night to the sage who is awake to the self.