Bhashya
‘तत् तस्मिन्नर्थे एष श्लोकः मन्त्रोऽपि भवति ।तदेव एति तदेव गच्छति, सक्त आसक्तः तत्र उद्भूताभिलाषः सन्नित्यर्थः ; कथमेति ? सह कर्मणा — यत् कर्म फलासक्तः सन् अकरोत्, तेन कर्मणा सहैव तत् एति तत्फलमेति ; किं तत् ? लिङ्गं मनः — मनःप्रधानत्वाल्लिङ्गस्य मनो लिङ्गमित्युच्यते ; अथवा लिङ्ग्यते अवगम्यते — अवगच्छति — येन, तत् लिङ्गम्, तत् मनः — यत्र यस्मिन् निषक्तं निश्चयेन सक्तम् उद्भूताभिलाषम् अस्य संसारिणः ; तदभिलाषो हि तत्कर्म कृतवान् ; तस्मान्तन्मनोऽभिषङ्गवशादेव अस्य तेन कर्मणा तत्फलप्राप्तिः ।तेन एतत्सिद्धं भवति, कामो मूलं संसारस्येति ।अतः उच्छिन्नकामस्य विद्यमानान्यपि कर्माणि ब्रह्मविदः वन्ध्याप्रसवानि भवन्ति, ‘पर्याप्तकामस्य कृतात्मनश्च इहैव सर्वे प्रविलीयन्ति कामाः’ इति श्रुतेः ।किंच प्राप्यान्तं कर्मणः — प्राप्य भुक्त्वा अन्तम् अवसानं यावत्, कर्मणः फलपरिसमाप्तिं कृत्वेत्यर्थः ; कस्य कर्मणोऽन्तं प्राप्येत्युच्यते — तस्य, यत्किंच कर्म इह अस्मिन् लोके करोति निर्वर्तयति अयम्, तस्य कर्मणः फलं भुक्त्वा अन्तं प्राप्य, तस्मात् लोकात् पुनः ऐति आगच्छति, अस्मै लोकाय कर्मणे — अयं हि लोकः कर्मप्रधानः, तेनाह ‘कर्मणे’ इति — पुनः कर्मकरणाय ; पुनः कर्म कृत्वा फला-
In plain words
On this point there is a verse — and it's scripture too, not just later teaching. 'He goes to exactly what he was attached to' — 'attached' simply means desire had taken hold of him toward that thing. How does he get there? 'Together with the action' — whatever he did while chasing its result, that very deed carries him to it; he ends up with its fruit. And what carries him? 'The mind is the sign' — mind is called the vehicle because it is the dominant part of the subtle body; or, put another way, it's called that because it is the very thing by which we infer what's going on inside someone — and that vehicle is fixed, firmly and decisively, on whatever this wandering soul desires. It was the wanting itself that drove the deed; so it is purely because the mind clung to that object that the person ends up reaping that fruit through that action. This settles it: desire is the root of the whole wandering existence. That's why, for someone who knows brahman and has cut desire off at the root, even the actions still sitting there go nowhere — they become as fruitless as a barren woman's child, just as scripture says: 'For one whose longing is satisfied, whose self is complete, every desire dissolves away right here.' And there's more: 'having reached the end of the action' means having lived it out completely — used up its fruit down to the last drop. Whose action's end is this? The action of whoever is doing something, anything, here in this world — once he has enjoyed its fruit fully and reached the end of it, he comes back from that other world to this one, in order to act again — because this world runs on action, which is exactly why the text says 'for action': to do it all over again. And having acted again, [taking in] its fruit—
Close to the Sanskrit
On this matter, this verse — which is also a Vedic mantra — occurs. 'He goes to that very thing, he attains that very thing' — 'attached' means 'clinging,' that is, being one in whom desire for it has arisen. How does he go? 'Together with the action' — whatever action he performed while attached to its fruit, together with that very action he goes to it; he attains its fruit. What is that [sign]? 'The sign is the mind' — because the mind is the chief element of the subtle body, the mind is called the 'sign'; or else, that by which one infers or understands is the 'sign,' and that is the mind — that on which this transmigrator's mind, in which desire has arisen, is firmly and decisively fixed. For it was desire for that object which made him perform that action; therefore, precisely because of the mind's attachment to it, he attains that fruit by means of that action. By this it is established that desire is the root of transmigratory existence. Therefore, for the knower of brahman whose desire has been cut off, even the actions that still remain become like the offspring of a barren woman, on the authority of the scriptural text: 'For one whose desires are fulfilled, whose self is accomplished, all desires dissolve away right here.' Further, 'having reached the end of the action' — 'having reached' means having enjoyed it up to its termination, that is, having brought the fruit of the action to completion. Of whose action's end is this said? Of that action which this person performs and carries out here in this world — having enjoyed the fruit of that action and reached its end, he comes back again from that world to this world, for action — for this world is one in which action predominates, and that is why the text says 'for action,' meaning: to perform action again. Having performed action again, [enjoying] its fruit—