BG 15.17

15.17 उत्तमः the Supreme? पुरुषः Purusha? तु but? अन्यः another? परमात्मा the highest? Self? इति thus? उदाहृतः called? यः who? लोकत्रयम् the three worlds? आविश्य pervading? बिभर्ति sustains? अव्ययः the indestructible? ईश्वरः Lord.Commentary Purushottama is beyond the universe though He pervades the three worlds. Therefore He is called the Supreme Being by the Vedas and men of this world. He pervades the three worlds and upholds them yet? He is not tainted by the world. He is above the world or worldliness.Just as the waking state is different from the dram or the deep sleep states? just as the orb of the sun is different from his rays or the mirage they casue? so also is the highest Purusha different from the perishable and the imperishable Purushas.The highest Purusha is the haven of peace. In Him all take their refuge and eternal rest. He is incomparable for He is selfcontained there is nothing like Him. He can only be compared to Himself. The imperishable Being (Akshara Brahman) Who is beyond the world and the Avyaktam (the Unmanifested) are essentially the same as the Purushottama Who transcends both the Kshara and the Akshara.The Purushottama is ite distinct from the two -- Kshara and Akshara. He is the Supreme Being. The physical body? the astral body and the causal body are also termed the Self. But these are secondary selves. Paramatma or the Supreme Self is the primary Self. Purushottama or Paramatma is the supreme or the highest when compared with the other secondary selves created by ignorance. He is the innermost consciousness of all beings. He is the support of everything. He is the Niyanta? the Inner Ruler. He is independent. Therefore He is known as the Supreme Self in the Vedanta.Anyah Another? ite distinct from the two.Lokatrayam The three worlds Bhuh (the earth)? Bhuvah (the midregion) and Svah (heaven) are the three worlds.Purushottama is further described as follows He is the imperishable and omniscient Lord Narayana Who permeates the three worlds by His vital energy and sustains them by His mere existence in them.Avyaya Imperishable? that which is free from the modifications such as birth? death? etc. Just as the king who rules his subjects and controls them is distinct from them? so also the Supreme Being Who is the ruler of the perishable and the imperishable is distinct from them. (Cf.VIII.20)

— vedicscriptures · exposition · source ↗

The idea of this verse is very nicely expressed in the Kaṭha Upaniṣad (2.2.13) and Śvetāśvatara Upaniṣad (6.13). It is clearly stated there that above the innumerable living entities, some of whom are conditioned and some of whom are liberated, there is the Supreme Personality, who is Paramātmā. The Upaniṣadic verse runs as follows: nityo nityānāṁ cetanaś cetanānām. The purport is that amongst all the living entities, both conditioned and liberated, there is one supreme living personality, the Supreme Personality of Godhead, who maintains them and gives them all the facility of enjoyment according to different work. That Supreme Personality of Godhead is situated in everyone’s heart as Paramātmā. A wise man who can understand Him is eligible to attain perfect peace, not others.

— vedicscriptures · exposition · source ↗