That imperishable end which is nirguna brahman is going to explain in next verse.
na tad bhāsayate sūryo na śaśāṅko na pāvakaḥ | yad gatvā na nivartante tad dhāma paramaṁ mama ||15.6||
Neither the sun, nor moon, nor fire, illumines that having gone to which, they do not return. That is my limitless abode.
The content of this verse is drawn from kathopanisad and mundakopanisad.
na tatra sūryo bhāti na candratārakaṁ
nemā vidyuto bhānti kuto’yamagniḥ |
tameva bhāntamanubhāti sarvaṁ
tasya bhāsā sarvamidaṁ vibhāti ||
Neither does the sun shine there, nor the moon with all the stars, nor does this lightning shine. What to say of this fire? Everything shines after him who alone shines. By His light all this shines variously.
This prayer is uttered during lamp waving upon the Lord in the puja. In the temple usually the statue of the Lord is being placed in the sanctum which relatively dark, therefore a lamp must be lighted to see the Lord’s form. During the process, the devotee saying that even sun, moon, stars or lightening can’t see the true nature of Īśvara, what to talk about this small lamp.
When a given object is said to be known/evident, it needs light to shine on it. Here even the sun which shines the entire earth can’t illumine the nature of Īśvara, because Īśvara is the basis which lends existence and consciousness to these manifested source of light as it were. This understanding is unfolded through method of discrimination between seer and seen - drk drśya vivekah. Any object become evident to us, we think it is because of the light that shines on it. But without sight, it is not known to us. In this case eye is the seer/revealer and object is the seen/revealed. But without mind backed up the sight, object also wouldn’t become evident to me, therefore in this level mind is the seer and eye is the seen.
Further without consciousness me, mind can’t operate at all, thus consciousness is the seer and mind is the seen. Is there anything to back up consciousness? No, consciousness is the source of light which makes others evident in the same time self evident. It is the ultimate seer. Therefore it is said here in the prayer that “everything shines after him who alone shines”, lending existence and consciousness to all beings, means beings are essentially non-different from brahman.
If me being self-evident because I am that cit-brahman, but there are many living beings here and each of us is clearly self-evident. Does it means there are many consciousness? No. There is only one consciousness, because of seeing from the stand point of confined upadhī (many bodies), it seems many, but in reality it is only one. Just like there are many pot spaces which in reality it is only one space.
Dhāma - an abode, a place which neither the sun, nor moon, nor fire can illumine - na tad bhāsayate sūryo na śaśāṅko na pāvakaḥ. Is it so dark that nothing can illumine? No, because it is the seer of the seen, where the seen is illumined, made evident by the seer. Consciousness is the ultimate seer, where nothing can make it evident except itself. It lends its existence to the mind, the senses and to the whole world. When everything is consciousness - me, how is it possible of returning, or even going to that place? Thus, those who “go there” (in figurative sense) do not return - na nivartante.