After describing the field of actions and the helpless plight of the living entities, Krishna now establishes His unique position as the external and the internal maintainer of everything.

First, Krishna establishes Himself as the external maintainer. That splendor of the sun (yad āditya-gataṁ tejo), which lights up the whole world (jagad bhāsayate ’khilam), as well as that splendor in the moon (yac candramasi) and the fire (yac cāgnau), we should know (viddhi) that (tat) to be Krishna’s (māmakam) splendor (tejo). (BG 15.12) And (ca), entering into each planet (gām āviśya), Krishna (aham) sustains (dhārayāmy) all the living beings (bhūtāni) with His strength (ojasā). And (ca), becoming (bhūtvā) the moon (somo), Krishna nourishes (puṣṇāmi) all (sarvāḥ) the herbs and the plants (auṣadhīḥ) forming their life-giving juice (rasātmakaḥ). (BG 15.13)

Now, Krishna reveals Himself as the internal maintainer. Becoming the fire of digestion (vaiśvānaro bhūtvā) situating Himself (āśritaḥ) in the bodies (deham) of the living entities (prāṇināṁ), Krishna (ahaṁ) digests (pacāmy) the four kinds of foodstuff (annaṁ catur-vidham) while keeping the balance (samāyuktaḥ) of the outgoing and incoming air of life (prāṇāpāna). (BG 15.14) Krishna’s maintenance goes even beyond the body. Krishna (ahaṁ) is furthermore (ca) situated (sanniviṣṭo) in everyone’s (sarvasya) heart (hṛdi), and from Krishna (mattaḥ) comes memory (smṛtir), knowledge (jñānam), and forgetfulness (apohanaṁ ca). Krishna is not only the source but also the object of knowledge. By all the Vedas (vedaiś ca sarvair), Krishna alone (aham eva) is to be known (vedyo). Krishna (aham) created Vedānta (vedānta-kṛd), and (ca) He alone (eva) is the knower of the Vedas (veda-vid). (BG 15.15)

Krishna is not only the maintainer of everything and everyone but His position as a maintainer is very unique. He is not to be equated with any one, either with the fallible or the infallible class. Hence, He alone is to be referred to as the Supreme Personality of Godhead. These (imau) are the two (dvāv) classes of beings (puruṣau) in existence (loke) – the fallible (kṣaraś) and the infallible (cākṣara eva ca). All living beings (sarvāṇi bhūtāni) are fallible (kṣaraḥ). However, the one in the liberated state (kūṭa-stho) is said to be (ucyate) infallible (akṣara). (BG 15.16) But (tu), the Supreme transcendental person (uttamaḥ puruṣas) is different (anyaḥ) – referred to (udāhṛtaḥ) as (iti) the Supreme Soul (paramātmā). He the inexhaustible (avyaya) Lord (īśvaraḥ), who (yo), entering the three worlds (loka-trayam āviśya) maintains them (bibharty). (BG 15.17)

Because (yasmāt) Krishna (aham) is Supreme (uttamaḥ), beyond (atīto) the fallible (kṣaram) and (ca) even (api) the infallible (akṣarād), He (asmi) is, therefore (ato) celebrated (prathitaḥ) in the world (loke) and (ca) in the Vedas (vede) as the Supreme Person (puruṣottamaḥ). (BG 15.18)

Whoever (yo) knows (jānāti) Krishna (mām) thus (evam) as the Supreme Person (puruṣottamam), without any doubt (asammūḍho), knows everything (sa sarva-vid) and whole-heartedly (sarva-bhāvena) engages in devotional service (bhajati) of Krishna (māṁ). (BG 15.19) Thus (iti), this is (idam) the most confidential (guhya-tamaṁ) scriptural injunction (śāstram), as spoken by Krishna (uktaṁ mayā). Understanding this (etad buddhvā), one becomes (syāt) intelligent (buddhimān), and accomplished (kṛta-kṛtyaś). (BG 15.20)