From Puruṣa came a brilliant golden egg. Taking this egg as a base, Puruṣa is re-born into creation. He first entered into the west, then into the nadir and finally to the east.
I feel like the dosage of depth is increased in this stanza. Look at the import! What can you understand? At first sight, barely can we understand anything. But as the intuition unfolds and help of Purāṇās, Brāhmaṇās, etc., come to our rescue, we will slowly see the true import rather than the apparent import. Let us look line by line now.
It seems that from Puruṣa is born a brilliant glowing egg. This in scriptures has many names: Hiraṇya Garbhāṇḍa, Brahmāṇḍa, etc. What is this egg? Last stanzas have suggested us that Puruṣa pervades the creation and enters into organic and inorganic materials. This stanza is like a prequel to the last few stanzas, for, this stanza pictorially tells us the birth of creation.
It is being stated that, Puruṣa was “As Is” when creation was naught. But when the parā vāk or the impulse to create occurred in Puruṣa, he gave rise to (Jāyata = give birth to) a brilliant EGG. Virāṭ = that which is glowing specially. This EGG can be seen as the EGG from which “Brahma” was hatched in the purāṇās like Bhāgavataṃ. Vēda and Purāṇa differs in the sense that, the absolute truth is conveyed in Vēda in their natural form while purāṇa conveys the same in a story form. The word Brahma = That which has property to expand (root: Bṛhmaṇaṃ) – is the creative force or impulse to create that occurs in the mind of Nārāyaṇa/Puruṣa. One can see the same story applied to even Garuḍa – The Eagle God in Bhāgavata (Garuḍōpākhyāna). So, why similar stories? What is that they want to so solidly convey through multiple repetitions? The fact that Puruṣa gives rise to a “Globe of creation” is the prime fact. When he gives rise to this EGG, HE fills the content of the EGG and spends time in it until it hatches.

‘Adhi’ means to take something as a base. So, they are saying that Puruṣa takes this brilliant EGG-Virāṭ as a base and is reborn (jātō – to take birth).
No! This is understanding of a linear mind. We should go beyond that. Let us take the birth of a hen for example. From a hen A, comes an egg B and from the egg B a chick C – which grows into a hen C. This cycle continues: A-B-C—-C-D-E—-E-F-G—-etc. Though the individual entities hen A and chick C change at every step of our cycle, the root principle of Parent-HEN and a Child-EGG does not change. These two entities are always there as long as the creation exists i.e., a parent gives rise to a child and a child grows into a parent (rather has capacity to grow into).

Compare the stanza to the above example. Puruṣa the Omniscient ONE gives rise to an egg and fills it with himself. From it, HE hatches himself as the baby-Puruṣa, the jīva. The 1st Puruṣa, let us call Puruṣa-1 and the 2nd Puruṣa as Puruṣa-2.
The same truth is conveyed in “Asya Vāmīya sūkta” or “Suparṇa Sūkta” of Rig Veda: “Two birds exist on the tree of LIFE. One bird always eats the fruits of the tree while the other bird just observes the first bird.” Bird-1 is the jīva who eats the fruits of his actions while the bird-2 is the Lord who just observed as one inside our heart – “I AM”.
In essence, Puruṣa-1 stays as background on which the drama of Puruṣa-2’s birth keeps happening. This is the meaning of the birth of Virāṭ from Puruṣa.
This line is understood as “ Sa Bhūmim Paścāt + Adah Purah Atyaricyata“. It seems that Lord first entered the West/past, then went deep into the Nadir/present and then finally came rising from the East/future. This is one of the most cryptic lines of this hymn. Paścha, Adhah and Purah can mean: WEST, Nadir and EAST or Past, present and future as well. Let us first take the spatial case with a vēdic injunction that –

As mentioned in my last stanza, the position of SUN has a link to human consciousness – (remember Inverted Tree?!).
1) WEST: It seems that GOD first entered WEST. So, where was he before? Here, GOD entered implies the entering of God-Consciousness as the “Awareness” of the beings of objective world. Before WEST, he is at the highest SKY possible i.e. ZENITH. This is the mid-noon to an observer on Equator. This NOON position is GOD’s abode in relation to understanding birth of consciousness. One can call this Vaikunṭha or Viṣṇu Lōka etc. Now, to create the cosmos, HE has to comedown. His descent is being stated as his entering into the WEST. Because this is his first descent, he starts his sleeping stage of awareness and hence the WEST implies “mineral kingdom”. So, Puruṣa vitalizes the minerals (an-aśana) first. It is ironic to see how “Western World” is mostly materialistic in “attitude” – maybe this property of Puruṣa acts in this way too! Its just my observation.
2) NADIR: Then after vitalizing the mineral kingdom, HE enters deep into the atoms of matter and causes a dreamy consciousness to them. This wakes the “Sāśana” aspect of plant kingdom. In plants, the pain and feeling is not localised but spread, as shown by Jagadish chandra bose and as postulated by many vēdic seers. Because GOD enters the “DEEP of NADIR”, i.e., plant kingdom too have the property of DEEP-Rootedness and hence the roots.
3) EAST: After dreamy state of NADIR, GOD awakens in animal consciousness. They form set-2 of “Sāśana”. Animals do have localised pain and pleasure and hence an awareness of surrounding, but not about themselves. This is representation of Puruṣa entering the EAST. As HE rises in the EAST, the whole creation wakes into an awareness of surroundings – A half-wake state with respect to a fully awakened spiritual state.
4) ZENITH: Consider the human consciousness. Humans are close to animals in the sense that, as long as they do not turn their “I AM” inward or towards the “I AM” in all, they behave like animals i.e., controlled by emotions and instincts. But when SUN rises from EAST and goes back to the abode of ZENITH or Vaikuntha, i.e., human reaches the full potential of his consciousness, HE becomes one with puruṣa.
So, in stage-1,2,3, human is Puruṣa-2 while in stage-4, he is Puruṣa-1.
What did we understand until now? Puruṣa-1 creates a brilliant EGG out of himself and hatches from it again as Puruṣa-2. This Puruṣa-2 is first sent to the WEST, then to the Nadir and to the EAST before reaching his FATHER, yet again!
If TIME is taken as our meaning, it would imply that the Puruṣa divided the Unlimited TIME into three parts of Past, present and future. That means, Puruṣa-2 gets the awareness of SPACE and TIME as he is hatched from the EGG.
At the end, it is stated that “Atyaricyata = Stood Beyond“. That means, even though Puruṣa is constrained by his own birth, he stood BEYOND this drama.