Link:- In the next verse, the Lord explains how the guns (modes of nature), evolved from prakrti, bind the spirit.
sattvam rajastama iti gunah prakrtisambhavah
nibadhnanti mahabaho dehe dehinamavyayam
Sattva, rajas and tamas - these guns (modes) born of prakrti, bind the imperishable spirit to the body, O mighty-armed. 5
Sattvarim rajastama iti ganah prakrlisambhavah:- The three gunas - sattva, rajas and tamas are born of peaked (primordial matter), which has been called 'Mahad Brahma, in the third and the fourth verses.
Here the term, 'Iti' (these) denotes, that these gulps (attributes or qualifies) out of which infinite universes evolve, and innumerable beings, diverse in character, are born, are neither more- or less, than three in number.
Nibadhnanti mahabaho dehe dehinamavyayam:- These three gums, bind the imperishable spirit, to the body. The fact is, that these gugas do not bind the spirit, but it is the spirit, which is bound by assuming its affinity with the gums and their evolutes - (objects, wealth, family and body etc.,). The spirit identifies itself, with the body and is attached to other persons and wealth etc. So in spite of being imperishable, it regards diseases and death of the body, as its own and also the loss of other persons and wealth etc., as its own.
It is a great wonder that the spirit in spite of being imperishable, immovable and uniform, being overpowered by guns and their propensities, itself becomes sattvika, rajasa and tamasa. Gosvdml Tulasidasaji also declares in 'the Manasa' that the spirit being a portion of the Lord, is imperishable, sentient, pure and naturally a mass of bliss (7/117/1).
Actually, the spirit is never bound by guns but when it assumes its affinity of 'I'ness, 'Mineness' and 'for me', with the body, it gets bound and the Lord seems to be attained with difficulty by it (Gita 12/5). Due to body consciousness, bound by the three auras, it cannot realize its immortality, which is beyond the three Gunas. The embodied soul, in spite of, being bound by three guns in fact remains as it is. It means, that it does not decay. So it is called 'Avyayam'.