After invoking the kṣatriya spirit of Arjuna and thus inspiring him to fight acknowledging his psychophysical nature, Krishna now begins to elevate Arjuna to a transcendental platform highlighting his duties as a spirit soul constitutionally. Thus, henceforward, Krishna takes us beyond the bodily conception of life. Krishna’s next instruction emphasizes the need for acting from the platform of duty.

Making (kṛtvā) happiness and distress (sukha-duḥkhe), gain and loss (lābhālābhau), victory and defeat (jayājayau) as equivalent outcomes (same) – Arjuna should thereafter (tato) engage (yujyasva) in fight (yuddhāya) and never incur sin (naivaṁ pāpam avāpsyasi). (BG 2.38)

This [the knowledge presented so far] has been described (eṣā te ’bhihitā) in terms of analytical study (sāṅkhye). However (tv), now, we should hear (śṛṇu) of it (imāṁ) in terms of buddhi yoga, or the yoga of intelligence (buddhir yoge). Being (yayā) engaged (yukto) with intelligence (buddhyā), we can get released from (prahāsyasi) the bondage of action (karma-bandhaṁ). (BG 2.39)

In this (iha) endeavor (abhikrama), there is (asti) no (na) destruction (nāśo) and there is (vidyate) no (na) diminution (pratyavāyo). Even a little (sv-alpam apy) application on this righteous path (asya dharmasya) releases (trāyate) one from the greatest fear (mahato bhayāt). (BG 2.40) What is the essence of this path of yoga of intelligence? Krishna reveals it now in this foundational verse of this chapter. The intelligence (buddhir) is resolute (vyavasāyātmikā) and the focus is one (ekeha). For the irresolute (avyavasāyinām), the intelligence (buddhayo) is surely (hi) many-branched (bahu-śākhā) and (ca) unlimited (anantāś). (BG 2.41)

In other words, in the yoga of intelligence, the intelligence carries (1) vyavasāyātmikā – the purity of purpose (resolute determination to act from our constitutional position as a spirit soul), and (2) ekeha – the clarity of goal (of extricating the soul from the clutches of matter).