In plain words
Of these, sattva, being pure, is luminous and free from affliction; yet it binds through attachment to happiness and attachment to jñāna, sinless one.
Word for word
Among them sattva, from its purity, [is] illuminating, free from affliction; it binds by attachment to happiness and by attachment to jñāna, O sinless one.
तत्र सत्त्वं निर्मलत्वात् प्रकाशकमनामयम्सुखसङ्गेन बध्नाति ज्ञानसङ्गेन चानघ
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
तत्र सत्त्वादीनां सत्त्वस्यैव तावत् लक्षणम् उच्यते —
निर्मलत्वात् स्फटिकमणिरिव प्रकाशकम् अनामयं निरुपद्रवं सत्त्वं तन्निबध्नाति । कथम् ? सुखसङ्गेन ‘सुखी अहम्’ इति विषयभूतस्य सुखस्य विषयिणि आत्मनि संश्लेषापादनं मृषैव सुखे सञ्जनम् इति । सैषा अविद्या । न हि विषयधर्मः विषयिणः भवति । इच्छादि च धृत्यन्तं क्षेत्रस्यैव विषयस्य धर्मः इति उक्तं भगवता । अतः अविद्ययैव स्वकीयधर्मभूतया विषयविषय्यविवेकलक्षणया अस्वात्मभूते सुखे सञ्जयति इव, आसक्तमिव करोति, असङ्गं सक्तमिव करोति, असुखिनं सुखिनमिव । तथा ज्ञानसङ्गेन च, ज्ञानमिति सुखसाहचर्यात् क्षेत्रस्यैव विषयस्य अन्तःकरणस्य धर्मः, न आत्मनः ; आत्मधर्मत्वे सङ्गानुपपत्तेः, बन्धानुपपत्तेश्च । सुखे इव ज्ञानादौ सङ्गः मन्तव्यः । हे अनघ अव्यसन ॥ ६ ॥
In plain words
Of sattva and the others, it is sattva's mark that is given first —
Sattva is like a crystal — clear, luminous, untroubled, free of any real flaw — and yet even this purest of the three still manages to bind. How? Through attachment to pleasure. Think of the thought 'I am happy.' Pleasure is really just an object; the Self is the true subject. What happens in that thought is that pleasure gets falsely fused onto the subject — that fusing, and nothing else, is what clinging to pleasure actually is. And that fusing is exactly what ignorance is. A property that belongs to an object simply cannot become a property of the subject — that's a basic rule. Desire and everything like it, all the way through steadiness, has already been shown to belong entirely to the field, the object — never to the knower. So it's ignorance alone, sattva's own built-in defect, this failure to tell object from subject, that makes pleasure — which was never really the Self's own nature — seem to stick to it. It makes the unattached Self look attached; it makes someone who has no pleasure of his own look as if he does. The very same thing happens with attachment to knowledge. 'Knowledge,' grouped here alongside pleasure, also belongs to the field — specifically to the mind, not to the Self at all; if it really belonged to the Self, attachment to it, and bondage through it, simply wouldn't be possible. Understand attachment to knowledge and the rest exactly the same way you understood attachment to pleasure. This is addressed to you, sinless one, free of vice.
Close to the Sanskrit
There, of sattva and the rest, of sattva alone, first, the defining mark is stated —
Sattva, luminous like a crystal gem because of its purity, free of affliction, free of disturbance, binds that kṣetrajña. How? By attachment to pleasure: in the notion 'I am happy', the bringing about of a fusion, in the subject, the Self, of pleasure, which is really an object — this is falsely, indeed, an attaching to pleasure. That is exactly ignorance. For a property of the object does not become a property of the subject. Desire and the rest, up through steadiness, have been declared by the Lord to be a property of kṣetra alone, the object. Therefore, by ignorance alone — which is sattva's own inherent property, characterized by the non-discrimination of object and subject — it causes clinging, as it were, to pleasure, which does not belong to the Self's own nature; it makes the Self appear attached, as it were; it makes the unattached one appear attached, as it were; it makes the one without pleasure appear as if possessing pleasure. Likewise, by attachment to knowledge: 'knowledge', by its association with pleasure here, is a property of kṣetra alone, the object, specifically of the inner instrument — not of the Self; for were it a property of the Self, attachment to it would be impossible, and so would bondage. Just as with pleasure, so with knowledge and the rest, attachment is to be understood. O sinless one, O one free from vice.