In plain words
Earth, water, fire, air, space, manas, buddhi, and ahaṅkāra—this is My Prakṛti divided eightfold.
Word for word
Earth, water, fire, air, space, manas and buddhi too, and ahaṃkāra: thus this prakṛti of Mine [is] divided eightfold.
भूमिरापोऽनलो वायुः खं मनो बुद्धिरेव चअहङ्कार इतीयं मे भिन्ना प्रकृतिरष्टधा
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
श्रोतारं प्ररोचनेन अभिमुखीकृत्याह —
भूमिः इति पृथिवीतन्मात्रमुच्यते, न स्थूला, ‘भिन्ना प्रकृतिरष्टधा’ इति वचनात् । तथा अबादयोऽपि तन्मात्राण्येव उच्यन्ते — आपः अनलः वायुः खम् । मनः इति मनसः कारणमहङ्कारो गृह्यते । बुद्धिः इति अहङ्कारकारणं महत्तत्त्वम् । अहङ्कारः इति अविद्यासंयुक्तमव्यक्तम् । यथा विषसंयुक्तमन्नं विषमित्युच्यते, एवमहङ्कारवासनावत् अव्यक्तं मूलकारणमहङ्कार इत्युच्यते, प्रवर्तकत्वात् अहङ्कारस्य । अहङ्कार एव हि सर्वस्य प्रवृत्तिबीजं दृष्टं लोके । इतीयं यथोक्ता प्रकृतिः मे मम ऐश्वरी मायाशक्तिः अष्टधा भिन्ना भेदमागता ॥ ४ ॥
In plain words
First he whets the listener's appetite and turns him to face what is coming — then he speaks:
'Earth' here doesn't mean the solid ground — it means earth in its subtle, originating form, exactly as the teaching that nature divides eightfold tells us. The same goes for water, fire, wind, and space: all of them mean their subtle root, not their visible form. 'Mind' means the deeper cause of ordinary mind — ego itself. 'Intellect' means what causes even that ego — the Great Principle. And 'ego,' strangest of all, actually means the unmanifest itself, still carrying ignorance within it. Think of food that's been mixed with poison — people just call the whole dish 'poison,' even though it's mostly food. In the same way, this unmanifest root, carrying the seed-impression of ego within it, gets called 'ego,' because it's the very thing that sets ego, and everything that follows from it, into motion. And ego really is the seed of all activity — anyone can see that, everywhere in the world. So this whole nature, described just as I've laid it out, is my own divine power of māyā, appearing here as eight distinct strands.
Close to the Sanskrit
Having made the hearer face-toward, by means of arousing interest, he says —
'Earth' — the subtle element of earth is meant, not the gross, because of the statement 'nature is divided eightfold.' Likewise, water and the rest too are meant only as subtle elements — water, fire, wind, space. 'Mind' — the cause of [ordinary] mind, ego, is understood. 'Intellect' — the cause of ego, the Great Principle. 'Ego' — the unmanifest joined with ignorance. Just as food mixed with poison is called 'poison,' so too the unmanifest, possessing the latent impression of ego, the root cause, is called 'ego,' because it is that which initiates ego. Ego alone, indeed, is seen in the world as the seed of all activity. Thus this nature, as has been described, is my, my, divine power of māyā, which has come, eightfold, into division.