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

Sūtra 9
jyotir upakramā tu tathā hy adhīyate eke
jyotiḥ-light; upakramā-beginning with; tu-indeed; tathā-in that way; hi-indeed;
adhīyate-iread; eke-some.
Light is its origin. Also, other passages confirm it.
Purport by Śrīla Baladeva Vidyābhūṣaṇa
The word tu (but) is used in the sense of certainty. The word light is used to
mean the Supreme Personality of Godhead. In this way He is celebrated in the
śruti-śāstra (Bṛhad-āraṇyaka Upaniṣad 10.4.16):
tad devā jyotiṣāṁ jyotiḥ
"The demigods meditate on Him, the light of lights."
The word upakrama should be understood here in the sense of "cause". Because
this aja (unborn) has Brahman as its cause, its being unborn is metaphorical only,
just as the "cup" in Bṛhad-āraṇyaka Upaniṣad 2.2.3.
In that passage it is said:
arvāg-bilaś camasa ūrdhva-budhna
"There is a cup with its mouth down and its bottom up."
As the "cup" here is actually the skull, in the same way the ajā (unborn) here is
not actually unborn, but is the potency born from Brahman, as is described in the
first and fourth chapters of Śvetāśvatara Upaniṣad.
The first quote is (Śvetāśvatara Upaniṣad 1.3):
te dhyāna-yogānugatā apaśyan
devātma-śaktiṁ sva-guṇair nigūḍhām