गोविन्द भाष्य (श्रील बलदेव विद्याभूषण - अचिन्त्यभेदाभेद वेदान्त ब्रह्मसूत्र भाष्य सटीक)

Purport by Śrīla Baladeva Vidyābhūṣaṇa
In this sūtra the word "aṇuḥ" (the atomic soul) should be understood from the
previous sūtra. In this sūtra the genitive case is used in the sense of the ablative.
The individual spirit soul is atomic and not all-pervading. Why is that? The sūtra
explains: "Because of departure, travel, and return."
In the Bṛhad-āraṇyaka Upaniṣad (4.4.2) it is said:
tasya haitasya hṛdayasyāgraṁ pradyotate. tena pradyotenaiṣa ātmā niṣkrāmati
cakṣuṣo vā mūrdhno vānyebhyo vā śarīra-deśebhyaḥ
"The soul shines in the heart. At the moment of death the effulgent soul leaves
through the opening of the eyes, the opening at the top of the the head, or another
opening in the body."
In the Bṛhad-āraṇyaka Upaniṣad (4.4.11) it is said:
anandā nāma te lokā
andhena tamasāvṛtāḥ
tāṁs te pretyābhigacchanti
avidvāṁso 'budhā janāḥ
"Sinful fools enter into planets known as the worlds of torment, full of darkness
and ignorance."
In the Bṛhad-āraṇyaka Upaniṣad (4.4.6) it is said:
prāpyāntaṁ karmaṇas tasya
yat kiñcedam karoty ayam
tasmāt lokāt punar etya
yasmai lokāya karmaṇe
"At the time of death the soul reaps the results of his works. He goes to the
world where he deserves to go. When the results of his past deeds are exhausted,
again he returns to the middle planets, the world of karma."
In this way the Bṛhad-āraṇyaka Upaniṣad describes the soul's travel from one
place to another. If he were all-pervading, the soul would not be able to travel from
one place to another, for he would already be everywhere.