The first issue the Gita must address is whether and to what extent there can be liberation from the binding action of the three Gunas of Nature; the second is what actually gets “liberated”; the third, the method of effecting this liberation; the fourth, once there is a liberation, what, if any, motive spring of action remains for the soul thus liberated; and fifth, what is there that exists outside the limitations and bonds of Prakriti and the Gunas.
These issues all have been previously introduced, and lines of understanding hinted at. While we have brought in the concept of the Purushottama previously, it must be noted that the Gita has not yet explicitly done so.
It is axiomatic in philosophy that one cannot truly observe and understand any system within whose framework one is limited; it requires a standpoint outside of that framework to look at it with an independent view. It is not surprising therefore, that the Gita takes the position that liberation is possible when one steps outside the framework of the active Nature and the Gunas that control everything there. Sankhya includes the reason, the ego-sense, the mind, the senses and the objects of the senses within the framework of what we may call the “lower nature”, and thus, it must develop both a method and an instrument that can exceed and escape the framework. The Gita finds this in the Akshara Purusha which by definition is uninvolved, separate, outside the action of the Gunas.
This brings us then to the issue of how action is possible when we shift to this outside, uninvolved standpoint. There seems to be no impetus to action contained there. It is for this reason that the Gita must bring in the concept of the Purushottama, so that it can bridge between the inactive Purusha (Akshara) and the active Purusha (Kshara) and provide thereby some means of developing action outside the framework of Prakriti and the Gunas, with the Divine now recognized as the Lord and Master of works.
Sri Aurobindo describes this: “Therefore by rising to him through the Self it is possible to have spiritual freedom from our works and yet to continue in the works of Nature.”
Sri Aurobindo, Essays on the Gita, Second Series, Part I, Chapter 1, The Two Natures, pp. 252-253