The Gita takes a somewhat different approach than classical Vedanta on the question of the reality of the manifestation and our action in the world. It does not treat the world as in illusion, or something to be rejected; rather, it accepts a basic reality to that manifestation, but at the same time points out that our existence is not limited by that reality, and that we are more than the complex of mind-life-body that we normally accept as the frame of our existence.
The issue then, for the Gita, is how we can shift our stance to the true inner Self and from there, how we can relate to the manifestation of Nature. The Gita accomplishes this by accepting the distinction between the Soul and Nature and showing that the Soul has multiple standpoints, one of which is involved in and bound by the actions of Nature; another which is independent of Nature, separate and aloof, and a third which recognizes both of these other two stances as aspects of its Oneness.
Nature, then, according to the Gita, is more or less a machinery operated by the three Gunas and consisting of the principles of Sankhya, the elements of matter which create outer forms, the senses that perceive and interact with them, the mind, the Reason and finally the spiritual consciousness. These are involved in the mechanical process, but evolve out as “…the soul in Nature becomes aware of itself by an upward evolution of each instrument…” as Sri Aurobindo indicates.
The Reason (Buddhi) disentangles itself from an exclusive preoccupation with the mechanical forms of the manifestation of Nature eventually, and begins to distinguish the higher spiritual principle as well. Sri Aurobindo describes the process: “In Vedantic language, it sees the spirit, the being; it ceases to identify itself with the instruments and workings of Nature, with its becoming; it identifies itself with its true Self and being and recovers its immutable spiritual self-existence. It is then from this spiritual self-existence, according to the Gita, that it can freely and as the master of its being, the Ishwara, support the action of its becoming.”
Sri Aurobindo, Essays on the Gita, First Series, Chapter 24, The Gist of the Karmayoga, pp. 240-241