15.20 This guhyatamam, most secret, i.e. most mystical;- what is that?-sastram, scripture-. Although the Gita as a whole is spoken of as the scripture, still this chapter itself is here referred to as such, and this for eulogy as is evident from the context. For, not only has the entire meaning of the scripture Gita been stated here in brief, but the whole purport of the Vedas also has been comprehended here. And it has been said, 'He who realizes it is a knower of the Vedas' (1), 'I alone am the object to be known through all the Vedas' (15). (Thus, this most secret scripture) iti uktam, has thus been uttered; maya, by Me; anagha, O sinless one.
O scion of the Bharata dynasty, buddhva, under-standing; etat, this, the scripture which has the purport as has been revealed; syat, one becomes; buddhiman, wise; and krta-krtyah, has his duties fulfilled; but not otherwise. The meaning is that what-ever a Brahmana has to do as a conseence of his special birth (as a Brahmana), all that becomes accomplished when the reality of the Lord is known. The idea is that nobody's duties become fulfilled in any other way. And it has been said, 'O son of Prtha, all actions in their totality culminate in Knowledge' (4.33). There is also a saying from Manu:
'This, verily, is the fulfilment of a Brahmana in particular. For, by getting this, a twice-born has his duties fulfilled; not otherwise' (Ma. Sm. 12.93).
Since you have heard from Me this truth about the supreme Reality, therefore, O scion of the Bharata dynasty, you have achieved your Goal!