If we look past the philosophical details to the underlying focus and action, we can see a lot of similarity between the Vedantic yoga of knowledge and the philosophy of the Sankhya. They both use the power of the intelligence, and the discriminating intellect to determine the underlying truth of existence, regardless of whether they consider that truth to be an illusory Maya or Prakriti consisting of the action of the 3 gunas.
Each of them sees liberation as the result of a process of abstraction from involvement in the works of the world, leading to a quiescent opening to a vast, unmoving, silent Reality, however it is actually described or defined. This provides us a basis for the Gita taking up the Sankhya and integrating it with the Vedantic path that is at its core.
The Gita adds to this path of knowledge, an emphasis on the value and importance of the Yoga of Works. Sri Aurobindo describes it this way: “But for the Yoga of the Gita, as for the Vedantic Yoga of works, action is not only a preparation but itself the means of liberation; and it is the justice of this view which the Gita seeks to bring out with such an unceasing force and insistence….”
The Gita brings about the integration of these diverse paths through a re-defining of the meaning of renunciation: “Renunciation is indispensable, but the true renunciation is the inner rejection of desire and egoism; without that the outer physical abandoning of works is a thing unreal and ineffective, with it it ceases even to be necessary, although it is not forbidden.”
Sri Aurobindo summarizes the integrated path of the Gita: “Knowledge is essential, there is no hgiher force for liberation, but works with knowledge are also needed; by the union of knowledge and works the soul dwells entirely in the Brahmic status not only in repose and inactive calm, but in the very midst and stress and violence of action. Devotion is all-important, but works with devotion are also important; by the union of knowledge, devotion and works the soul is taken up into the highest status of the Ishwara to dwell there in the Purushottama who is master at once of the eternal spiritual calm and the eternal cosmic activity.”
Sri Aurobindo, Essays on the Gita, First Series, Chapter 9, Sankhya, Yoga and Vedanta, pp. 79-80,