The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
5. (There are personal conductors) because that is established on the ground of both (i.e. road and travellers) being bewildered (i.e. unconscious).
As, owing to their separation from a body, the organs of those who go on the road beginning with light are wrapped up, they are incapable of ruling themselves; and the light &c., as they are without intelligence, are equally incapable. Hence it follows that the particular intelligent deities who represent light and the rest are appointed to the conductorship. For in ordinary life also drunken or senseless people whose sense-organs are wrapped up follow a road as commanded by others.--Again light and the rest cannot be taken for marks of the road because they are not always present. A man who dies in the night cannot come to day in its true (physical) nature; and he cannot wait (for the break of day), as we have already explained above (IV, 2, 19). But this objection does not apply to gods who are permanent. And gods may be called light and so on, because they represent light and so on. Nor is the expression, 'From light to day,' &c. objectionable, even if we adopt the sense of conductorship; for it means, through the light as cause they come to the day; through the day as cause, to the waxing half of the moon. And such instruction is seen also in the case of conductors known in ordinary life, for they say, Go hence to Balavarman, thence (i.e. Balavarman conducting you) to Gayasimha, thence to
[paragraph continues] Krishnagupta. Moreover, in the beginning where the text says that they go to the light, a relation in general only is expressed, not a special relation; at the end, however, where it is said he leads them to Brahman, a special relation is expressed, viz. that between conducted and conductor. Therefore this is accepted for the beginning also.--And as the organs of the wandering souls are wrapped up together there is no possibility of their enjoying anything. Although, however, the wanderers do not enjoy anything, the word 'world' may be explained on the ground that those worlds are places of enjoyment for other beings dwelling there--The conclusion therefore is that he who has reached the world of Agni is led on by Agni, and he who has reached the world ruled by Vâyu, by Vâyu.
But how, if we adopt the view of conductorship, can this apply to Varuna and the rest? Varuna and the rest were inserted above the lightning; but scripture states that after the lightning until Brahman is reached a person leads who is not a man.--To this doubt the next Sûtra replies.