15.20 iti thus, guhyatamam most secret, śāstram science (teaching), idam this, uktam has been taught, mayā by Me, anagha O sinless one, ētat buddhvā knowing this, buddhimān wise, syāt will become, kṛtakṛtyaḥ (who has) accomplished all the duties, ca and, bhārata O harata.

Commentary:
Guhyatamam: Most profound secret.uddhiman means here a knower of the Self or Atmart.The knowledge of the Self which gives emancipation from the round of birth and death, and freedom from the bonds of Karma is eulogised in this verse. If this most profound teaching is rightly understood, known or realised, it makes a man wise and gives him illumination. After this there is nothing left for him to know or strive for. He has reached the goal of life or the aim of human existence. He has arrived at the end of his journey. His endeavour for Self-realisation is over. He has attained perfection. He has complete knowledge of the Supreme eing. He gets rahma Jnana. He moves in the consciousness of the Divine. He beholds the Self everywhere. He lives in rahman. He regards all activities as His divine play.When one realises rahman, he has discharged all the duties of life. He is liberated from the bonds of Karma. He becomes a Jivanmukta or illumined sage who has transcended the body-consciousness, the three alities of Nature, the three states of consciousness (wakeful state, dream and deep sleep), the pairs of opposites and the cycle of birth and death. He knows fully well that rirth has been destroyed, that what has to be done has been accomplished, that life's highest goal has been reached and that he has nothing more to do or to learn. He has understood the profound mystery of life -- the riddle of this universe. He is a Sarvavit or all-knower.The whole of the Gita is called science, yet the fifteenth discourse alone is here declared as the science for the sake of eulogising it. The fifteenth discourse contains the intessence of the Gita, the Upanishads and the Vedas. This is the butter churned from the milk of the Vedas. It has been said that, "He who knows the peepul tree knows the Veda" (XV.1). The Lord has also said, "It is I Who am to be known by all the Vedas" (XV.15). Only when a man knows this science as taught above does he become wise -- but not otherwise. Whatever duty a rahmana of the highest birth has to do, all that has been doen when one attains the knowledge of the Self. "All actions in their entirety culminate in knowledge" (IV.33). "This is the fulfilment of the birth, particularly of a rahmana; because the twice-born accomplishes all his duties only by attaining to this, but not otherwise", says Manu Smriti.As you have heard from Me this truth about the Supreme eing, you are a happy man and you have done all your duties; you have attained Self-realistion.y using the words Anagha and harata, Lord Krishna hints that even when an ordinary man who knows this fifteenth discourse can attain knowledge of the Self and become a Kritakritya, then what to say of Arjuna who was sinless and who was born in a noble family with divine attributes The Lord, by using the word Anagha, also indicates that the Guru who is a knower of rahman should instruct the most profound secret (the science of the Self) only to alified persons who are free from impurities of the heart or tossing of the mind, who are calm and endowed with the four means of salvation. The man of impure mind will not be able to grasp the truth. The sinful man with his perverted intellect will distort the truth and thus pave the way for the destruction of himself and his followers.Thus in the Upanishads of the glorious hagavad Gita, the science of the Eternal, the scripture of Yoga, the dialogue between Sri Krishna and Arjuna, ends the fifteenth discourse entitled:The Yoga of the Supreme Spirit. ,,