Verse 15·18

यस्मात्क्षरमतीतोऽहम् अक्षरादपि चोत्तमः ।अतोऽस्मि लोके वेदेच प्रथितः पुरुषोत्तमः ॥

yasmātkṣaramatīto’ham akṣarādapi cottamaḥato’smi loke vedeca prathitaḥ puruṣottamaḥ

The doctrine of the Gita from the beginning to the end converges on all its lines and through all the flexibility of its turns towards one central thought, and to that it is arriving in all its balancing and reconciliation of the disagreements of various philosophic systems and its careful synthetising of the truths of spiritual experience, lights often conflicting or at least divergent when taken separately and exclusively pursued along their outer arc and curve of radiation, but here brought together into one focus of grouping vision. This central thought is the idea of a triple consciousness, three and yet one, present in the whole scale of existence.
There is a spirit here at work in the world that is one in innumerable appearances. It is the developer of birth and action, the moving power of life, the inhabiting and associating consciousness in the myriad mutabilities of Nature; it is the constituting reality of all this stir in Time and Space; it is itself Time and Space and Circumstance. (Kshara)

But then there is another spirit of whom we become aware and who is none of these things, but self and self only. This Spirit is eternal, always the same, never changed or affected by manifestation, the one, the stable, a self-existence undivided and not even seemingly divided by the division of things and powers in Nature, inactive in her action, immobile in her motion. (Akshara)

The Purushottama is in the heart of every creature and is manifested in his countless Vibhutis; the Purushottama is the cosmic spirit in Time and it is he that gives the command to the divine action of the liberated human spirit. He is both Akshara and Kshara, and yet he is other because he is more and greater than either of these opposites.