न तद्भासयते सूर्यो न शशाङ्को न पावक: |
यद्गत्वा न निवर्तन्ते तद्धाम परमं मम || 6||
na tad bhāsayate sūryo na śhaśhāṅko na pāvakaḥ
yad gatvā na nivartante tad dhāma paramaṁ mama
na—neither; tat—that; bhāsayate—illumine; sūryaḥ—the sun; na—nor; śhaśhāṅkaḥ—the moon; na—nor; pāvakaḥ—fire; yat—where; gatvā—having gone; na—never; nivartante—they return; tat—that; dhāma—abode; paramam—supreme; mama—Mine
Neither the sun, nor the moon, nor the fire can illumine that (state of Paramatma), which having reached, (men) do not return (take birth again); That is My Supreme Abode.
The Sun, Moon and Fire illumine the material objects. The eye illumines the Sun; and the buddhi (intellect) illumines the eye; and Atma illumines the intellect (buddhi). So the whole universe including the shining objects like the Sun and the Moon, are illumined by perceiving senses and the intellect, which receive their light ultimately from Atma. So Atma is the light that illumines everything. All other things shine by the reflected light of Atma. In the Mundakopanishad this is clearly explained and proved (Na tatra suryo bhati).
Yad gatva na nivartante: Those who have reached the state of Atma do not again fall into the miserable pit of Samsara. From any other world in the universe, man has to return and take birth again. They have not the power to end sorrow. Only Paramatma has that power. The blessed state of Self-realisation, full of bliss, is Moksha. The same idea has been expressed in the previous verse also. (Yasmin gata na nivartanti bhuyah)