These bright and dark paths of the world are regarded as eternal. One takes the seeker to the Supreme and the other brings back the votary again and again to where he started.
Krishna conclusively says that these white and black paths, Uttarāyaṇa and Dakshiṇāyana, are eternal. They are not related to the sun or its seeming courses, which are not, however, uniform in the world, as in the case of day and night. Sun lights only half the earth at a time. Day here is night there. The northward and southward courses also are not accurately the same in both hemispheres.
Spirituality presents uniform, eternal truths, values and propositions. The two paths, spirituality posits, are of knowledge and of ignorance, of discrimination and of delusion.
Discriminate the imperishable inner presence, the Soul. Outlive concepts like getting born, dying, getting to heavens, etc. Regard the life here on earth as an experience and occasion to elevate yourself from the clutches of the ephemeral to the embrace of the Eternal, and realize the outcome here and now.