Verse 3.1.7

बृहच्च तद्दिव्यमचिन्त्यरूपं सूक्ष्माच्च तत्सूक्ष्मतरं विभाति ।
दूरात्सुदूरे तदिहान्तिके च पश्यन्त्विहैव निहितं गुहायाम् ॥ ७ ॥

bṛhacca taddivyamacintyarūpaṃ sūkṣmācca tatsūkṣmataraṃ vibhāti |
dūrātsudūre tadihāntike ca paśyantvihaiva nihitaṃ guhāyām || 7 ||

7. That shines as vast, heavenly, of unthinkable form and subtler than the subtle, much farther than the distant, near, also here, and seen fixed in the cavity, by the intelligent. (7)

Shankara’s Commentary:

Com.—The Brahman now treated of and attainable by truth, etc., is vast, because it is all-pervading; ‘heavenly,’ self-luminous and imperceivable by the senses. Therefore alone, is it that its form is unthinkable; it is subtler than even the subtle, such as the akas and the rest; for, being the cause of all, it is of unsurpassing subtlety. Vibhati, shines diversely, i.e., in various forms such as that of the sun, the moon, etc. Again it is farther, even from the most distant places; for, the Brahman cannot be in the least approached by the ignorant. It is also near, i.e., in the body itself; because, it is the atman of those who know and because it is within all, from the Sruti which declares it to be even within the akcas. ‘In those who see,’ among the intelligent men. ‘Fixed,’ seated, i.e., seen by yogis, as possessed of the activity of seeing, etc. Where? in the cavity, i.e., in the intellect; for, it is seen as lodged there by those who know; still, though lodged there, it is not seen by the ignorant, as it is veiled by ignorance.