I will now declare to thee, O best of the Bharatas, at what time yogins dying obtain freedom from, or subjection to rebirth. Fire, light, day, the fortnight of the waxing moon, six months of the sun's northern course — going then and knowing the Supreme Spirit, men go to the Supreme. But those who depart in smoke, at night, during the fortnight of the waning moon, and while the sun is in the path of his southern journey, proceed for a while to the regions of the moon and again return to mortal birth. These two, light and darkness, are the world's eternal ways; by one a man goeth to return not, by the other he cometh back again upon earth. (Chapter viii, Judge's recension)
This paragraph must have many meanings, some of them general, some more in detail, the latter being the most difficult to put down on paper. Speaking generally the two paths of Pravrittimarga and Nivrittimarga are here referred to. One is the pathway of light and immortality; the other the dark way that leads to re-embodiment.
In the words of the Bhagavad-Gita man may "unite himself with Brahman" and thus become an immortal spiritual being in the cosmos, no longer subject to reincarnation, nor to the trials of human life. He attains to this state by following the pathway of life. The training and discipline for disciples of this pathway are given in the Bhagavad-Gita. It is the pathway Krishna is recommending to Arjuna throughout the work. On the other hand, concentrate energies on the matter-side and revel in material existence, and man will continue to be bound to the wheel of rebirth with its accompanying duality of pleasure and pain. These two pathways are eternal in manifested existence, although at different cycles there is a predominance of the influence of one or the other. To paraphrase the last sentence in the quotation: "These two, light and darkness, are the world's eternal ways; by the light path a man goeth never to return [as a human being], by the dark path he cometh back [into incarnation] again upon earth."
Words are not wasted in the Bhagavad-Gita, each one has its purpose and meaning. For instance when the Northern and Southern Solsticial pathways are spoken of, there is clear reference to the fact that in normal death egos leave the earth through the lunar or southern pathway, and this journey has much to do with the Kama-loka, where the Inner Man sheds his gross (lunar) bodies preparatory to post-mortem peregrinations. And the Northern Solstice refers to the pathway of initiation by which the initiant ascends to Light and Spirit, never to return as a human being — but as a god.
The various terms, such as "fire," "light," "day," and "smoke," "night," etc., all have their meanings in painting a detailed picture of what is spoken of above. They refer, in the words of the commentary (S. D., I, 86), to the "names of various deities which preside over the Cosmo-psychic Powers." The bright array of deities are those belonging to the Hierarchy of Compassion, the Agnishwattas, the Manasaputras, etc., and the dark or lunar deities refer to the lunar side of Nature and ourselves. Man is a compound of both sides. He has two paths before him.