BG Chap 13 - The cause of jīva's association with prakṛti
The cause is beginningless desire of the jīva for objects made of the guṇas (kāraṇaṁ guṇa-sango’sya). Though the soul does not actually contact the body, the contact is fabricated thru ignorance. He traps himself in the repeated cycle of birth and death, and by his attempt to enjoy matter, he becomes matter and experiences change – birth, death, old age and disease – though he is changeless. The jīva is contaminated with beginningless imprints in the form of karma. The jīva, being an enjoyer, desiring enjoyable objects takes shelter of prakṛti equipped with the desirables which she offers to him, until those imprints are destroyed by devotee association. With the destruction of impressions, he enjoys happiness in the abode of the Lord.
The jīva, identifying with his body produced by prakṛti, experiences happiness and distress, which are born from prakṛti. Though the jīva is by nature knowledge and bliss, he is situated in prakṛti (puruṣaḥ prakṛti-stho hi) due to his impressions of beginningless karma, where he imagines himself as a puruṣa. Endowed with body, senses and prāṇa, which are produced by material nature, and which the jīva rules, he experiences happiness and distress produced by prakṛti. Thus incarcerated and suffering within matter, the jīva focuses his attempt on the impossible: enjoying by exploiting creations of the guṇas. He experiences happiness and suffering by taking births in high positions (devas and men) or lower (animal, bird and others), and in noble and degraded forms.