Prior to the Gita, the traditions of India had reached a barrier which created an insuperable gulf between the true spiritual principle and what necessarily needed to be called the illusory construction of Nature based working through the three Gunas. Sankhya included the material elements, the objects of the senses, the senses themselves, the perceiving mind, the reason and the ego-sense all as part of Nature, Prakriti. The Soul was bound to the action of these elements and thereby misled by the illusion of reality that they impart. The solution provided was to disentangle the consciousness from the action of Prakriti and to identify with the divine consciousness that was outside of, unmoving and unaffected by Nature. This division or duality however, led to the downgrading of the world of action to the status of a dream, an illusion, something that must be avoided, denied and eventually parted company with.
We see the attempt of the Vedantic tradition to begin the process of healing this duality, as the Upanishads repeatedly tell us that there is only one Spirit, and of that one Spirit everything exists. “One without a second” and “All this is the Brahman.” However, the Upanishads, being more mystical in their nature rather than an intellectual exposition, were unable to entirely resolve the concerns and the traditional practice went on essentially with the idea of a permanent duality between the material nature and the spiritual being.
The Gita took up the challenge by pointing out that the resolution of the apparent contradiction must come through moving our view to the place where material nature and spiritual nature are not in conflict. Sri Aurobindo describes the solution provided by the Gita: “There is a supreme nature of the Divine which is the real source of cosmic existence and its fundamental creative force and effective energy and of which the other lower and ignorant Nature is only a derivation and a dark shadow. In this highest dynamis Purusha and Prakriti are one. Prakriti is there only the will and the executive power of the Purusha, his activity of being,–not a separate entity, but himself in Power.”
Sri Aurobindo, Essays on the Gita, Second Series, Part I, Chapter 1, The Two Natures, pp. 254-255