In plain words
Sattva, rajas, and tamas—the guṇas born of Prakṛti—bind the imperishable embodied one to the body, mighty-armed one.
Word for word
Sattva, rajas, tamas: [these] guṇas born of prakṛti bind, O mighty-armed one, the imperishable embodied one in the body.
सत्त्वं रजस्तम इति गुणाः प्रकृतिसम्भवाःनिबध्नन्ति महाबाहो देहे देहिनमव्ययम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
के गुणाः कथं बध्नन्तीति, उच्यते —
सत्त्वं रजः तमः इति एवंनामानः । गुणाः इति पारिभाषिकः शब्दः, न रूपादिवत् द्रव्याश्रिताः गुणाः । न च गुणगुणिनोः अन्यत्वमत्र विवक्षितम् । तस्मात् गुणा इव नित्यपरतन्त्राः क्षेत्रज्ञं प्रति अविद्यात्मकत्वात् क्षेत्रज्ञं निबध्नन्तीव । तम् आस्पदीकृत्य आत्मानं प्रतिलभन्ते इति निबध्नन्ति इति उच्यते । ते च प्रकृतिसम्भवाः भगवन्मायासम्भवाः निबध्नन्ति इव हे महाबाहो, महान्तौ समर्थतरौ आजानुप्रलम्बौ बाहू यस्य सः महाबाहुः, हे महाबाहो देहे शरीरे देहिनं देहवन्तम् अव्ययम् , अव्ययत्वं च उक्तम् ‘अनादित्वात्’(भ. गी. १३ । ३१) इत्यादिश्लोकेन । ननु ‘देही न लिप्यते’(भ. गी. १३ । ३१) इत्युक्तम् । तत् कथम् इह निबध्नन्ति इति अन्यथा उच्यते ? परिहृतम् अस्माभिः इवशब्देन निबध्नन्ति इव इति ॥ ५ ॥
In plain words
So what exactly are these guṇas, and how do they actually bind someone? Here's the answer.
Sattva, rajas, tamas — those are their names. And notice: 'guṇa' here is a special, technical word, not the ordinary sense of quality that depends on some substance, the way color depends on a colored thing. There isn't meant to be any real gap here between a quality and whatever supposedly has it. So really, these guṇas only seem eternally dependent on kṣetrajña — because their whole relationship to it is made of nothing but ignorance — and only in that sense do they seem to bind it. What actually happens is this: the guṇas lean on kṣetrajña as their support and, by doing that, secure their own continued existence — that leaning is all 'binding' really means here. And these guṇas, arising from prakṛti, ultimately from the Lord's own māyā, seem to bind — O mighty-armed one (an epithet, by the way, for someone whose arms are so strong and long they reach down to the knees) — they seem to bind the embodied being, the one who wears a body, right there within that body, even though this being is actually imperishable, exactly as already proven in the verse beginning 'because of beginninglessness.' But wait — didn't we already say 'the embodied one is not tainted'? So how can it now be said, seemingly the opposite, that the guṇas 'bind' it? That was already taken care of: notice the little word 'as it were' sitting right there in 'they bind, as it were.' Nothing was ever said without that qualification.
Close to the Sanskrit
What are the guṇas, and how do they bind? — this is now stated —
Sattva, rajas, tamas — these are their names. 'Guṇas' is a technical term; the guṇas here are not, like color and the rest, dependent on a substance. Nor is any real difference between guṇa and its possessor intended here. Therefore the guṇas, being eternally dependent, as it were, on kṣetrajña, because of being of the very nature of ignorance with respect to kṣetrajña, bind kṣetrajña, as it were. Having made him their basis, they regain their own existence — this is what is meant by 'they bind'. And they, arisen from prakṛti, arisen from the Lord's own māyā, bind, as it were, O mighty-armed one — mahābāhu meaning one whose two arms are great, exceptionally capable, hanging down to the knees — O mighty-armed one, they bind the embodied one, the possessor of a body, within the body, though he is imperishable; and his imperishability was already stated by the verse beginning 'because of beginninglessness' (Bhagavad Gītā 13.31) and so on. Objection: it was stated, 'the embodied one is not tainted' (Bhagavad Gītā 13.31). How then is it said here, differently, that they bind? This has already been resolved by us through the word 'as it were': 'they bind, as it were.'