Verse 3.12.3

या वै सा पृथिवीयं वाव सा यदिदमस्मिन्पुरुषे शरीरमस्मिन्हीमे प्राणाः प्रतिष्ठिता एतदेव नातिशीयन्ते ॥ ३.१२.३ ॥

yā vai sā pṛthivīyaṃ vāva sā yadidamasminpuruṣe śarīramasminhīme prāṇāḥ pratiṣṭhitā etadeva nātiśīyante || 3.12.3 ||

3. That which is this earth is this human body, because all the prāṇas are based in this body and cannot exist independent of it.

Word-for-word explanation:

Yā vai sā pṛthivī, that which [has earlier been referred to as] this earth; iyam vāva sā, it is that; yat idam asmin puruṣe śarīram, the body which is associated with a human being; hi, because; asmin, on this [body]; ime prāṇāḥ, these prāṇas [i.e., prāṇa, apāna, etc., and also the five elements—ākāśa, vāyu, etc.]; pratiṣṭhitāḥ, are based; etat eva na atiśīyante, they cannot go beyond this [body—i.e., they cannot exist independent of this body].

Commentary:

The earth is the gāyatrī and this gāyatrī is also the human body because the human body is born of the earth. How is the human body borm of the earth? This body is made up of the same elements (space, air, fire, etc.) that the earth is. The five prāṇas (prāṇa, apāna, vyāna, udāna, and samāna) are also known as elements, and they rest on this body. The body is therefore the gāyatrī like the earth. It is the gāyatrī because the prāṇas cannot exist without the body.