एषा तेऽभिहिता साङ्ख्ये बुद्धिर्योगे त्विमां श्रृणु ।
बुद्ध्या युक्तो यया पार्थ कर्मबन्धं प्रहास्यसि ।। २-३९ ।।

eṣā te’bhihitā sāṅkhye buddhir-yoge tv-imāṁ śṛṇu |
buddhyā yukto yayā pārtha karma-bandhaṁ prahāsyasi || 2.39 ||

Having concluded the Sankhya exposition, Krishna proceeds to present his unique message on Yoga (Karmayoga). It should be emphasized that Karmayoga, as presented by Krishna in Bhagavad Gita, is unique in its philosophy and pursuit. It is a novel interpretation of the Upanishadic knowledge, not found explicitly in any of the earlier texts. In fact the apoorvata (uniqueness) of Bhagavad Gita lies in its presentation of the Karmayoga as a full-fledged pursuit of mind and intelligence (buddhi). And this new relevance is significantly indicated right in the introductory verse (2.39):

एषा तेऽभिहिता सांख्ये बुद्धिर्योगे त्विमां श्रृणु ।
बुद्‌ध्यायुक्तो यया पार्थ कर्मबन्धं प्रहास्यसि ।।

Mark the words : “I shall explain to you the WISDOM (buddhi) relating to Karmayoga. Equipped with this WISDOM (buddhi), you will be able to cast aside the bondage of all karmas.” The emphasis is not on external karma, but on the internal yoga-buddhi.

There is a common misunderstanding. The general belief is that while in Sankhya pursuit the practitioner has to ruminate and introspect ceaselessly on the Reality, in Karmayoga it is the pursuit of action that counts. Pursuit of action every one does. All who do karma are not karmayogins! The karmayogin differs from all other performers of actions in so far as his mind and intelligence are able to feel and understand a transcendental relevance and purpose behind each and everything he does. The transformation in his attitude or outlook is brought about by the intelligence. The wisdom about Karmayoga gained by the intelligence, and its relentless application while doing any karma whatsoever, is what distinguishes the karmayogin from all other performers.

Like Sankhya, karmayoga too is a full-fledged buddhi-based pursuit. In Sankhya, the basic contemplation is that of the unborn, non-acting and un-dying Soul. In karmayoga, the basic pursuit is the keen observation of the mind’s responses to a host of interactions, and their constant sublimation by activating the yoga-buddhi, the samatva-buddhi. That is why in later chapters (verse 5.5), Krishna likens Sankhya to Yoga: