In plain words
One whose every undertaking is free from desire and self-willed projection, whose actions have been burned in the fire of jñāna, is called wise by those who know.
Word for word
Whose undertakings are all free of desire and intention, him, whose actions are burned by the fire of knowledge, the wise call a paṇḍita.
The commentators
Bhagavadgītābhāṣyam
तदेतत् कर्मणि अकर्मदर्शनं स्तूयते —
यस्य यथोक्तदर्शिनः सर्वे यावन्तः समारम्भाः सर्वाणि कर्माणि, समारभ्यन्ते इति समारम्भाः, कामसङ्कल्पवर्जिताः कामैः तत्कारणैश्च सङ्कल्पैः वर्जिताः मुधैव चेष्टामात्रा अनुष्ठीयन्ते ; प्रवृत्तेन चेत् लोकसङ्ग्रहार्थम् , निवृत्तेन चेत् जीवनमात्रार्थम् । तं ज्ञानाग्निदग्धकर्माणं कर्मादौ अकर्मादिदर्शनं ज्ञानं तदेव अग्निः तेन ज्ञानाग्निना दग्धानि शुभाशुभलक्षणानि कर्माणि यस्य तम् आहुः परमार्थतः पण्डितं बुधाः ब्रह्मविदः ॥ १९ ॥
In plain words
Now this very thing is praised: seeing non-action in action —
For whoever sees things as just described, every undertaking — every action taken up — is free of desire and intention: free, that is, of the desires and the intentions behind them. Such actions are simply carried out as bare gestures with no purpose of their own — if by someone still engaged in the world, for the world's welfare; if by someone withdrawn, merely to keep the body alive. Such a person's actions are burnt by the fire of knowledge: seeing inaction within action, and the like, is that knowledge, and that knowledge itself is the fire. By that fire of knowledge, all actions, whether marked auspicious or inauspicious, are burnt away. Whoever this is true of — him the wise, the knowers of Brahman, call truly wise.
Close to the Sanskrit
That very this — the seeing of non-action in action — is praised —
Of whoever sees as has been stated, all — whatever undertakings — all actions, that are undertaken, [are called] 'undertakings'; free of desire, intention: free of desires and their causes, intentions — they are performed merely as mere purposeless gestures; if by one engaged, for the welfare of the world; if by one withdrawn, for the sake of mere subsistence alone. Him, whose actions are burnt by the fire of knowledge — the seeing of inaction and the like in action and the like is knowledge; that very [knowledge] is the fire; by that fire of knowledge, actions, however marked as auspicious or inauspicious, are burnt — of whom this is so, him the wise, the knowers of Brahman, truly call wise. || 19 ||