Around 800 B.C.E. the age of philosophy arose almost simultaneously throughout the ancient world. In Greece, the Middle East, India, and China the sages, who were always the inward-looking psychonauts,  began to think about the way we think. Prior to this time, all religious practices were outwardly focused. The tools of religion, the rituals, and sacrifices were designed to barter and bargain with the elements of nature and the gods. The assumption was – if we conducted these sacrifices for the benefits of the gods, they would be pleased, and in turn would do us favors. The favors sought were of three kinds: rewards of health, wealth, and progeny. We all want to be healthy, to have lots of money, and lots of children. Enlightenment, three thousand years ago, was not a goal. At best one might hope to be taken to a heavenly reward after this life, but even this was a later religious invention.
Religion always distances the seeker from that which is sought. Religious rituals and sacrifices require intermediaries – priests, to act on the behalf of the petitioners. Direct connection to the divine is not possible, save for those very rare sages to whom the gods revealed the original truths in the first place.
In most of these ancient religions the gods, being metaphors for the elements of nature, were numerous, powerful, and capricious. They were not great examples of moral behavior. They were more like arrogant, narcissistic bigger brothers and sisters who could make life miserable for you if you didn’t stay out of their way or keep them happy. Even in the earliest monotheistic religions, God was a stern taskmaster who had to be pleased and appeased in order for your life to be peaceful.
With the dawning of philosophy, the focus turned inward. The external powers of nature were seen as reflections of the inner world, and vice versa. External sacrifices and rituals became internalized. No longer were the gods out there; they were metaphors for what was happening in here. No longer did you need a priest to talk for you to the divine – the divine already resided inside you; you needed to do the work yourself. A map to self-realization, or more correctly Self-realization, was required to help guide you on the path, but you had to walk the path.
One such map became very influential in India around the time of the Buddha. It explained the inner and outer workings of the mind and the world. While the map didn’t answer all the questions, and everyone did not accept some of the answers it did produce, it was the most comprehensive model yet devised. It became the foundation for yogic and Buddhist cosmology. It was the Samkhya psychocosmological model. 
We will leave it to the historians to argue whether Samkhya created this model, and thus can be considered the father of the yogic model that followed it, or whether there was an earlier version from which both Samkhya and yoga evolved, thus making the two brothers, rather than father and son. For our purposes it is enough to know that both Samkhya and Classical Yoga, from which all other yogas evolved (especially the Tantra and Hatha yogas most practiced today), share this same psychophysical view of the universe.
Our brief journey into the Samkhya philosophy begins with looking at the two great divides upon which the model is founded: purusha (soul) and prakriti (nature).