In plain words
Neither sun, moon, nor fire illumines that. Having reached it, none return. That is My supreme abode.
Word for word
Not that does the sun illumine, nor the moon, nor fire; having gone to which [they] do not return, that [is] My supreme abode.
न तद् भासयते सूर्यो न शशाङ्को न पावकःयद्गत्वा न निवर्तन्ते तद् धाम परमं मम
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
तदेव पदं पुनः विशेष्यते —
तत् धाम इति व्यवहितेन धाम्ना सम्बध्यते । तत् धाम तेजोरूपं पदं न भासयते सूर्यः आदित्यः सर्वावभासनशक्तिमत्त्वेऽपि सति । तथा न शशाङ्कः चन्द्रः, न पावकः न अग्निरपि । यत् धाम वैष्णवं पदं गत्वा प्राप्य न निवर्तन्ते, यच्च सूर्यादिः न भासयते, तत् धाम पदं परमं विष्णोः मम पदम् , ॥ ६ ॥
In plain words
The same term is now taken up once more and given a sharper definition —
The word 'abode' here links up with another 'abode' that appears later in the same sentence, even though other words come between them. This abode, made entirely of light, this state, cannot be illumined even by the sun, by Āditya himself, for all his power to light up everything else. The moon can't illumine it either, nor can fire, nor flame. This is the very abode, belonging to Viṣṇu, that once you reach it, once you attain it, you never leave again — and it is the very abode that the sun and every other light in the sky cannot illumine. That abode, that state, is Viṣṇu's supreme state. It is my own state.
Close to the Sanskrit
That very term is again being specified —
'That abode' connects with the other occurrence of 'abode' placed at a distance [in the sentence]. That abode, of the nature of light, [that] state, the sun, [i.e.] Āditya, does not illumine, even though possessing the power to illumine everything. Likewise, the moon does not, nor does fire, nor even flame. Which abode, belonging to Viṣṇu, [that] state, having gone to, having attained, they do not return; and which the sun and so on do not illumine — that abode, [that] state, is the supreme [state] of Viṣṇu, My state.