Verse 6.8.6

तस्य क्व मूलं स्यादन्यत्राद्भ्य्ऽद्भिः सोम्य शुङ्गेन तेजो मूलमन्विच्छ तेजसा सोम्य शुङ्गेन सन्मूलमन्विच्छ सन्मूलाः सोम्येमाः सर्वाः प्रजाः सदायतनाः सत्प्रतिष्ठा यथा तु खलु सोम्येमास्तिस्रो देवताः पुरुषं प्राप्य त्रिवृत्त्रिवृदेकैका भवति तदुक्तं पुरस्तादेव भवत्यस्य सोम्य पुरुषस्य प्रयतो वाङ्मनसि सम्पद्यते मनः प्राणे प्राणस्तेजसि तेजः परस्यां देवतायाम् ॥ ६.८.६ ॥

tasya kva mūlaṃ syādanyatrādbhy'dbhiḥ somya śuṅgena tejo mūlamanviccha tejasā somya śuṅgena sanmūlamanviccha sanmūlāḥ somyemāḥ sarvāḥ prajāḥ sadāyatanāḥ satpratiṣṭhā yathā tu khalu somyemāstisro devatāḥ puruṣaṃ prāpya trivṛttrivṛdekaikā bhavati taduktaṃ purastādeva bhavatyasya somya puruṣasya prayato vāṅmanasi sampadyate manaḥ prāṇe prāṇastejasi tejaḥ parasyāṃ devatāyām || 6.8.6 ||

6. Where else, except in water, can the body have its root? O Somya, when water is the sprout, 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. As to how, O Somya, these three deities [fire, water, and earth] enter a body and each becomes threefold, this has already been explained. O Somya, as this person is dying, his speech merges into the mind, his mind into prāṇa, his prāṇa into fire, and then fire merges into Brahman, the Supreme Deity.

Word-for-word explanation:

Tasya, of it [the body]; adbhyaḥ, [besides] from water; anyatra kva, where else; mūlam syāt, can the root [of the body] be; somya, O Somya; adbhiḥ śuṅgena, with water as the sprout; 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; yathā nu khalu, as to how; somya, O Somya; imāḥ tisraḥ devatāḥ, these three deities [fire, water, and earth]; puruṣam prāpya, enter a person; ekaikā bhavati, each one becomes; trivṛt trivṛt, threefold; tat uktam purastāt eva bhavati, this has been explained already; somya, O Somya; asya puruṣasya prayataḥ, as this person is dying; vāk, the organ of speech; manasi sampadyate, merges into the mind; manaḥ prāne, the mind into prāṇa; prāṇaḥ tejasi, prāṇa into fire; tejaḥ parasyām devatāyām, fire into the Supreme Deity [Brahman],

Commentary:

What happens when a person dies? First, his speech merges into his mind. He cannot speak any more, but his mind is still active. Sometimes when a person has a stroke, he cannot speak but his mind is alert. Then the mind merges into prāṇa, his life force. The mind ceases to function, but he is still breathing. Then prāṇa merges into fire. Fire here means the heat in the body. If the body is still warm, you