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

Godhead has entered the cave of the heart:
taṁ durdarśaṁ gūḍham anupraviṣṭaṁ
guhāhitaṁ gahvareṣṭhaṁ purāṇam
adhyātma-yogādhigamena devaṁ
matvā dhīro harṣa-śokau jahāti
"The Supreme Personality of Godhead, who is the oldest person, and who is
worshiped in the jungle of this world, remains hidden in the cave of the heart. A
wise man, meditating on Him in a trance of spiritual yoga, gives up all material joy
and grief."
The word hi (indeed) in this sūtra means "This is indeed corroborated by all the
Purāṇas." The word pibantau (they both drink) in the passage of the Upaniṣad is
used in the same sense as the phrase "the two parasol-bearers." Although only one
of the pair carries the parasol, they are still known as "the two parasol-bearers." In
the same way only one of the two "drinkers" here actually drinks. The word chāyā-
tapau (shade and light) here means either that the knowledge of the two persons is
different, or it means that one of the persons is bound to the cycle of repeated
birth and death and the other is free from the cycle of repeated birth and death.
Sūtra 12
viśeṣaṇāc ca
viśeṣaṇāt—because of distinctive qualities; ca—also.
Also because of the differences between them.
Purport by Śrīla Baladeva Vidyābhūṣaṇa
In this section of Kaṭha Upaniṣad the jīva and the Supreme Personality of
Godhead are carefully distinguished, the jīva described as the meditater and the
Supreme Personality of Godhead as the object of meditation. Thus is Kaṭha
Upaniṣad 1.2.12 quoted above they are carefully distinguished: one as the
meditater and the other as the object of meditation. In Kaṭha Upaniṣad 1.3.1 in the
words chāyā-tapau (shade and light) they are again distinguished: one being all-
knowing and the other having only a small sphere of knowledge.
Kaṭha Upaniṣad 1.3.9 explains:
vijñāna-sārathir yas tu