hetuh prakritir ucyate
purushah sukha-duhkhanam
bhoktrtve hetur ucyate

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

There are Two versions of this sloka. One is Kaarya -kaarana [கார்ய காரண कार्य कारण] and the other is Kaarya -karana [கார்ய கரண कार्य करण]. Better is Kaarya'kaarana. Karya indicates the body and kaarana indicates the Eleven organs in the body [Five karmendriya, Five Gyanendriya and Mind]. Kartrtve = their actions [of the body and the Eleven organs], hetu = cause, prakruti = body. Therefore, for the activities of body and the organs, cause is body itself. We will explain this shortly. So, for all actions body is responsible. Due to these actions there will be results. Purusha = atman, sukha-dukhanam = happiness and sorrow [as results of the actions of the body], bhoktrtve = experiences, hetu = cause. ucyate = is told. So, for all activities, body is the cause; but the consequent pleasures and miseries are experienced by atman. Thus there is division of work between atman and body. From this we have to understand that action is possible only when atman and body are associated; similarly, experience is possible only when atman and body are associated; not otherwise. Body alone can never act nor experience the happiness and sorrow. Atman, if it wants to experience, has to deploy body as an instrument. Thus this instrument body is the cause for actions. But a body without soul can never act. This we see in reality. So we have to interpret that a body with soul, only acts. On the other hand, atman by itself can never experience pleasures and pains. Though atman only experiences, as atman alone has Gyana, it requires a body to feel. So, atman, in a body experiences the happiness and sorrow. Though body is subject to activities like listening to music or eating food, it is atman, which enjoys the experience. Thus in this association of a body and a soul, the body is cause for all actions and atman is cause for all feelings.