कार्यकारणकर्तृत्वे हेतुः प्रकृतिरुच्यते।
पुरुषः सुखदुःखानां भोक्तृत्वे हेतुरुच्यते।।13.21।।
।।13.21।।प्रकृति और पुरुष -- दोनोंको ही तुम अनादि समझो और विकारों तथा गुणोंको भी प्रकृतिसे ही उत्पन्न समझो। कार्य और करणके द्वारा होनेवाली क्रियाओंको उत्पन्न करनेमें प्रकृति हेतु कही जाती है और सुखदुःखोंके भोक्तापनमें पुरुष हेतु कहा जाता है।
The word karya meaning effect refers to the physical body. The word karana means the instrument of action denoting the senses of perception, the organs of action and the mind. In the activation of both karya and karana to function the atma or immortal soul alone is the cause. This confirms that all manifest activity by which the jiva or embodied being experiences existence is dependent upon prakriti or the material substratum pervading physical existence which is predicated by the impulses of the atma. The atma merely performs its natural function as monitor and director of the jiva in all respects. Affirmation of this is given in the following Vedic aphorism found in the Vedanta Sutra II:III.XXXX beginning krita prayatna apekesah meaning the Supreme Lord induces the atma to act according to the effects experienced by the jiva so that there is no contradiction in the prohibitions and injunctions of the Vedic scriptures. The function of the atma is to witness the karma or reactions to ones actions and govern the jiva effects of karma as they evolve and grow. The atma being embodied is the sole cause for a jiva to experience joy and grief through the medium of matter. Thus the difference in function in regard to both the atma and the physical body has been briefly elaborated seperately and in conjunction. The process by which the inherently pure and spiritual atma which is most blessed comes to experience pleasures and pain derived from contact with products of matter is through the three gunas being modes of goodness, passion and ignorance which are effects of prakriti and figuratively symbolise all derivatives of matter as all matter is within the purvey of the three gunas. Here in this verse the word purusa is referring to His expansion as the atma within the heart of all living entities which by its own intrinsic nature is liberated and blissful but by the influence of karma and prakriti is entangled in the material existence undergoing experiences of enjoyment and suffering based on this relationship which manifest according to the dicitates and constraints of the adventitiously and contrary circumstances of past actions from which arise effects known as karma. The word bhoktrtve meaning the experience of happiness and distress confirms this.