Meaning:
The knowledge by which all life forms – animals, human-beings and the gods – project the ‘I’ consciousness, by which the mind, the organs of perceptions and such otherwise insentient bodies appear to become alive, and which is the source of light yet being eclipsed by the very mind that is lit due to its presence, that is the supreme knowledge and whoever has the steadfast contemplation and complete gratification on this wisdom is the preceptor. This is my determinate knowledge or conclusive wisdom.

First Line:
yaa = Which (knowledge); thiryag = (in) animals; nara = human-beings; dhaevathaa bhir = gods and all; aham ithy amthah = (creates) the existence of “I”; sphutaa = clearly; grihyathae =realized;

Second Line:
yadh bhaasaa = by which means; hridhaya aksha dhaeha vishayaa = mind, eye and such instruments of perception, gross body and things; bhaanthi = perform the functions; swatho chaethanaah = insentient bodies acquire intelligence;

Third Line:
thaam = that the Atman (is like); bhaasyaih = (the illumination of which shows the existence of) organs of perception; pihitha = clouding; arkamandala = the Sun; nibhaam = This is an example; sphoorthim = This complete and everlasting (the Atman); sadhaa bhaavayan = whoever holds forever in their contemplation;

Fourth Line:
yogee = yogi who is absorbed in the complete knowledge; nir vritha = perfectly happy; maanaso hi = within the mind; gurur iti = is the real preceptor; yaesha = who inculcates this concept; maneesha mama = my determinate knowledge or conclusive wisdom.

Interpretation
It appears that the fourth and final verses are declared to expand on the knowledge already revealed in the first two verses.
Is the ‘I’ consciousness applicable only to human-beings? Or is it true for all life-forms? Besides independent of the ‘I-consciousness’, the instruments such as the mind and the organs of perceptions are also seem to have their own local intelligence.

These doubts are clarified in the first two lines of this verse.

The notion of ‘I’ exists in all lives. That is how, according to their embodiment in the world, these life-forms behave. But the ego or ‘I’ which is the identification with the bodies is not real. The true ‘I’ is the Self, which is the infinite-knowledge.
Only due to the Self, the mind, the organs and the bodies come to life. Only the light of the Self shines through the mind and body. Without the light of the Self, all these are unanimated and insentient.

A doubt is raised.

If the Self is light eternally shining within, why is not directly comprehensible? It is because it is eclipsed by the mind. How can the mind eclipse the Atman? If the mind itself is lighted by the Atman, how is it possible for the mind to hide the view of Atman?

Jagadguru Adi Sankara shows an example to explain this.

The Sun cannot be hidden by the clouds. Yet we speak of the Sun being hidden by the cloud, only to mean that the cloud is blocking our view of the Sun. The cloud does not and cannot hide the Sun. In fact, even the existence of the cloud is due to the light of the Sun only. Similarly, the mind exists only due to the Atman. Yet, due to Avidya or ignorance, the mind is blanketing our comprehension of the Self.

Whoever understands this and completely contemplates on this wisdom, he alone is the yogi and the preceptor, who is absolutely fulfilled. This is the

Manisha of Sankara that is revealed in this verse.

The absolute-bliss is the ultimate benefit of Self-realization. This is indicated here and further explained in the next and final verse.