13:20  

कार्यकरणकर्तृत्वे हेतुः प्रकृतिरुच्यते ।
पुरुषः सुखदुःखानां भोक्तृत्वे हेतुरुच्यते ॥१३- २०॥

kaaryakaraNakartRRitwe hetuH prakRRitiruchyate ।

puruShaH sukhaduHkhaanaaM bhoktRRitwe heturuchyate ॥१३- २०॥

Source: Automatic ITRANS Transliteration

The performance of actions, agency, is said to be nature's purpose.
The experiencing of pains and pleasures is said to be Person's purpose.

Source: Milind S. Pandit

The Prakriti is said to be the cause of production of physical body and organs (of perception and action). The Purusha (or the consciousness) is said to be the cause of experiencing pleasures and pains.

Source: The Bhagavad-Gita: The Sacred Song

Nature is said to be the cause of all material activities and effects, whereas the living entity is the cause of the various sufferings and enjoyments in this world.

Source: Bhagavad Gita As It Is