The pada describes what happens at death. Speech merges into the mind, the mind into prana, prana into the jiva, and the jiva with them into the subtle elements. Up to the path, knower and ignorant depart alike. The subtle body lasts until liberation, and the sutras note that for the knower of the highest Brahman there is no going out, as the Shruti says of the one without desire; the pranas merge in Brahman there. For the one who meditates on the qualified Brahman, the light of the heart brightens and the soul leaves by the hundred and first nadi, at the crown of the head. It follows the rays of the sun, even at night, and even when dying in the sun's southern course.
At death speech merges in mind, because this is seen and because scripture says so. The dying first stop speaking while the mind still works; the Chandogya says 'speech merges into mind'. Its functions merge, not the organ itself.
For the same reason all the other senses follow speech and merge in the mind. Sight, hearing and the rest withdraw their working into the mind at the time of departure.
That mind merges in prana, the vital breath, as the next clause of scripture shows: 'mind into breath'. Even after the mind stops working, breathing continues for a while.
That prana merges in the ruler of the body, the individual soul, because scripture speaks of the breaths gathering round him and going with him. The jiva carries them as it departs.
The soul with prana then rests in the subtle elements, for scripture says 'breath into fire'. Fire here stands for all the subtle elements that form the seed of the next body.
Not in one element only, for both scripture and smriti show that the body is made of all of them. The departing soul abides in the subtle elements together.
The mode of departure is the same for the knower of the qualified Brahman and the ignorant up to the start of the path; the immortality spoken of is relative, gained without burning away the subtle body.
That merging is until final release from samsara, for scripture speaks of continued worldly existence. The subtle elements merged in the Supreme are not dissolved absolutely before true liberation.
The subtle body is fine in size and in substance, for so it is perceived. Being minute and transparent, it is not seen leaving, yet it carries the soul onward.
And the warmth of the living body belongs to this subtle body, for that is reasonable. While it stays the body is warm; when it leaves, the body turns cold.
If it is said that scripture denies departure for the knower, no: the denial concerns the embodied soul. Acharyas differ here: some read 'his pranas do not go out' as no departure at all, others as the breaths not leaving the soul.
For in the recension of some it is clearly stated. The Madhyandina text of the Brihadaranyaka plainly says of the knower: 'his pranas do not depart; being Brahman, he goes to Brahman'.
The soul's abode, the heart, lights up at its tip; by that lit doorway, through the power of knowledge and remembrance of the path, favoured by the Lord in the heart, it leaves by the hundred-and-first nadi, the one going to the crown.
निशि नेति चेन्न सम्बन्धस्य यावद्देहभावित्वाद्दर्शयति च
niśi neti cenna sambandhasya yāvaddehabhāvitvāddarśayati ca
If it is said that one dying at night cannot follow the rays, no: the link between nadi and rays lasts as long as the body, and scripture shows it. The knower reaches the goal whatever the hour.
For the same reason, even one who dies during the southern course of the sun reaches the fruit of his knowledge. The season of death does not cancel it.
The smriti rule about the northern course is given for yogis, and these two paths belong to smriti. The Gita's teaching on the time of departure applies to yogis of smriti, not to knowers of the Upanishadic meditations.
Text source: Wikisource · CC BY-SA 4.0 (Wikisource transcription of a public-domain text)