The Gita clearly does not teach a doctrine of world-renunciation. The Gita does not accept a duality or some kind of irreconcilable gulf between the manifestation and the divine consciousness; rather it sees everything as one integrated whole, a divine Being that holds within itself both the manifest and the unmanifest in Oneness.
Sri Aurobindo describes the actual role of sages and yogis who achieve the state of nirvana: “Thus Nirvana is clearly compatible with world-consciousness and with action in the world. For the sages who ossess it are conscious of and in intimate relation by works with the Divine in the mutable universe; they are occupied with the good of all creatures….They have not renounced the experiences of the Kshara Purusha, they have divinised them; for the Kshara, the Gita tells us, is all existences…and the doing universal good to all is a divine action in the mutability of Nature. This action in the world is not inconsistent with living in Brahman, it is rather its inevitable condition and outward result because the Brahman in whom we find Nirvana, the spiritual consciousness in which we lose the separative ego-consciousness, is not only within us but within all these existences, exists not only above and apart from all these universal happenings, but pervades them, contains them and is extended in them.”
“Nirvana when we gain it, enter into it, is not only within us, but all around…because this is not only the Brahman-consciousness which lives secret within us, but the Brahman-consciousness in which we live. It is the Self which we are within, the supreme Self of our individual being but also the Self which we are without, the supreme Self of the universe, the self of all existences. By living in that self we live in all, and no longer in our egoistic being alone; by oneness with that self a steadfast oneness with all in the universe becomes the very nature of our being and the root status of our active consciousness and root motive of all our action.”
The essence then of Nirvana is the establishment of a new standpoint or status of consciousness that sees and acts from the basis of Oneness, not duality, and because of this Oneness, our entire life becomes divinised when we act with that awareness.
Sri Aurobindo, Essays on the Gita, First Series, Chapter 23, Nirvana and Works in the World, pp. 226-227