sattvam rajas tama iti
dehe dehinam avyayam
Material nature consists of three modes—goodness, passion and ignorance. When the eternal living entity comes in contact with nature, O mighty-armed Arjuna, he becomes conditioned by these modes.
Commentary by Srila Prabhupada
The living entity, because he is transcendental, has nothing to do with this material nature. Still, because he has become conditioned by the material world, he is acting under the spell of the three modes of material nature. Because living entities have different kinds of bodies, in terms of the different aspects of nature, they are induced to act according to that nature. This is the cause of the varieties of happiness and distress.
Commentary by Sri Visvanatha Cakravarti Thakur
After the Lord has described the appearance of all the living entities through prakrti (mother) and purusa (father), how are the gunas to be described? What type of bondage arises for the jiva from association with these gunas? This verse answers these questions.
In the body, the product of prakrti, the gunas bind up the jiva (dehinam) situated there by identification with it, due to the association with the gunas arising from beginningless ignorance, even though the jiva actually is without change (avyayam) and not attached.