dvāv imau puruṣau loke kṣaraś cākṣara eva ca |
kṣaraḥ sarvāṇi bhūtāni, all the things that you see in the world are because Purusha is mobile. If He was not mobile, the mobile world would not exist. So:
kṣaraḥ sarvāṇi bhūtāni, but kūṭa-stho ’kṣara ucyate || (XV, 16)
But that which is immobile, kūṭa-stho, that which transcends all movement, that which is above movement is akṣara, beyond the movement that is the immobile.
So, you have a contradiction here: the Reality is at once kṣara, and akṣara. Now, the reconciliation takes place between the two in the nature of Reality, which is above both movement and immobility and that is in the 17th verse:
uttamaḥ puruṣas tv anyaḥ: anyaḥ the other one however, there is still another one; kṣara is one, akṣara is another and there is still another; uttamaḥ puruṣas tv anyaḥ: there is still another, uttama, the supreme, there is uttama Purusha; paramātmety udāhṛtaḥ, He has been described as paramātman,
yo loka-trayam āviśya bibharty avyaya īśvaraḥ ||17|| (XV)
“He enters into all the 3 worlds and pervades, avyaya, yet He is inexhaustible, imperishable, even the whole world moves out of Him, He Himself enters into this…”
Now here, when you say: ‘He enters into this world’, we remember in the 9th chapter, He says: ‘they are in Me, but I am not in them’, here He says: ‘I am in them, yo loka-trayam āviśya, I have Myself entered into all the three worlds; bibharty avyaya īśvaraḥ, He is mobile, He throws Himself out and yet He is avyaya, He remains un-expended. One who expends Himself constantly, yet He remains un-expended.
And then He gives the name in the 18th verse:
yasmāt kṣaram atīto ’ham akṣarād api cottamaḥ |
ato ’smi loke veda ca prathitaḥ puruṣottamaḥ ||18|| (XV)
The name given to Himself is: “I am Purushottama because yasmāt kṣaram atīto, I am more than kṣara, I am more than ‘mobility’, I am more than akṣarād api, I am more than ‘immobile’; My immobility does not exhaust Me, My mobility does not exhaust Me. He is the Purushottama; ato ’smi loke veda ca prathitāḥ, in the people and also in the Veda therefore I am described as Purushottama, I am described therefore as Purushottama.”
Now, these three verses give us a complete description of the nature of the ultimate Reality. As I said it starts with the Veda, same concept; same concept is also repeated in the Upanishad: “tadejati tannaijati”. And now here you get a complete exposition of it, clear enunciation of it: “I am 3 Purushas”, that is to say, “although I am one, I am three-fold.” In other words the Reality is of such a nature, it is capable of different statuses. Just as I gave the example of ‘cooking and looking after the child’, the same person has two statuses, and without loosing the other, it is at the same time the other one. This capacity of becoming three-fold, four-fold…in fact it is also said: sahasra akśaḥ, He is also thousand-fold, there is also the Vedic concept: so, you may become million-fold, billion-fold and yet it remains the same Reality. Such is the mystery and wonder of that Reality.