Later on we learn Apara Prakriti consists of Tamas, Rajas, Sattwa, it’s a mixture of Sattwa, Rajas and Tamas of which these are the 8 elements, but Para Prakriti consists of Sat–Chit–Ananda: that is the real nature of divine nature. The lower nature, the Apara Prakriti consists of mortality. The higher nature is immortal, is imperishable, immortality, amṛtaṁ. That is why in the Veda it is declared: you as far as ‘you’, individual, are concerned you are ‘amṛtasya putrāḥ’ (Shvet. Upn. 2. 5): “you are the children of amṛta”, of the immortal. So, this is one answer to the question as to ‘who am I?’.
Now, in the 15th chapter, we have another answer as to ‘who am I’? verse n°7. Now, here the description is of the supreme Lord. In the 7th chapter we had the description of the Prakriti, of the power of the Divine. Here now, we have the description of the Divine Himself:
mamaivāṁśo jīva–loke jīva–bhūtaḥ sanātanaḥ |, this individual is mamaivāṁśo, “I am Myself that Jiva”. In the 7th chapter we had the description: jīva–bhūtāṁ: that is Prakriti herself is Jiva, the supreme Prakriti, divya Prakriti, divya power. Here, “I have Myself become the Jiva”, mamaivāṁśo sanātanaḥ, this is eternal: that is ‘you as an individual are an eternal portion of the supreme Lord Himself’.
If you combine these two propositions together you find that Jiva is at once the portion of the Supreme and something that is constituted by the supreme power: Supreme Being and supreme power. The individual share therefore both the aspects: the being of the supreme Lord and the power of the supreme Lord. Reality also itself is also Supreme Being and supreme power: when we say Reality is Sat and Chit, (Chit is power, Sat is being). So, when we say: Reality is Sat–Chit; it means the Reality is at once Supreme Being and also supreme power. And individual is the aṁśa of Supreme Being and supreme power. So, when you put both the statements together, you get the correct answer to the question as to ‘who am I’? “I am the portion of the supreme Being and the supreme Power”.
Therefore, just as the Reality is at once static and dynamic, even so, ‘I’ too is at once static and dynamic. Every individual therefore shares in the nature of the supreme Reality: I am also immobile and mobile; I am myself the supreme Lord, or supreme Lord Himself is myself, but aṁśa, the only difference between Him and me is that I am only a portion.
But basically the stuff is the same: the fire and the spark, the basic nature is the same; the ocean of water and the bubble, the nature is the same, (whether you drink one bubble or you drink the whole ocean, experience is of the same nature).
Now, this is the first part of my preface, because this chapter as I said is one of the most important chapters of the Bhagavad Gita, it tells you the entire story of creation; it describes the whole Reality, describes where I am in this Reality, in what way I am bound, why am I in bondage, why do I feel so restrained, full of suffering, sorrow, painful, why do I feel? And what is the means by which I can be liberated from it: the entire story is given in these brief twenty verses of this chapter.