तस्य क्व मूलं स्यादन्यत्रान्नादेवमेव खलु सोम्यान्नेन शुङ्गेनापो मूलमन्विच्छाद्भिः सोम्य शुङ्गेन तेजो मूलमन्विच्छ तेजसा सोम्य शुङ्गेन सन्मूलमन्विच्छ सन्मूलाः सोम्येमाः सर्वाः प्रजाः सदायतनाः सत्प्रतिष्ठाः ॥ ६.८.४ ॥
tasya kva mūlaṃ syādanyatrānnādevameva khalu somyānnena śuṅgenāpo mūlamanvicchādbhiḥ somya śuṅgena tejo mūlamanviccha tejasā somya śuṅgena sanmūlamanviccha sanmūlāḥ somyemāḥ sarvāḥ prajāḥ sadāyatanāḥ satpratiṣṭhāḥ || 6.8.4 ||
4. Where else, except in food, can the body have its root? In the same way, O Somya, when food is the sprout, search for water as the root; when water is the sprout, O Somya, search for fire as the root; when fire is the sprout, O Somya, search for Sat [Existence] as the root. O Somya, Sat is the root, Sat is the abode, and Sat is the support of all these beings.
Tasya, of it [the body]; annāt, [besides] from food; anyatra kva, where else; mūlam syāt, can the root [of the body] be; evam eva khalu, in this way; somya, O Somya; annena śuṅgena, with food as the sprout; apaḥ mūlam, water as the root; anviccha, search for; adbhiḥ śuṅgena, water as the sprout; somya, O Somya; tejaḥ mūlam, fire as the root; anviccha, search for; tejasā śuṅgena, fire as the sprout; somya, O Somya; sat mūlam, Sat [Existence] as the root; anviccha, search for; somya, O Somya; imāḥ sarvāḥ prajāḥ, all these beings; sat mūlam, have Sat as the root; sat āyatanāḥ, Sat as the abode; sat pratiṣṭhāḥ, Sat as the support.
Where there is a sprout, you know there is a root. Similarly, where there is a body, you know there is a root—that is, a source, and that source is food. Then what is the root of food? It is water. Again, water has its root in fire, and fire has its root in Existence.
The Upaniṣad gives a number of links here. They follow one after another. But the ultimate root, the ultimate source, is Sat, Existence—pure Spirit. All beings—men, women, children, trees, animals, everything—are based on Sat. Praja means what is born. All that are born (sarvā prajā) are dependent on and resting on Sat.