Bhagavad Gita Chapter 8, Verse 2

श्रीभगवानुवाच | अक्षरं ब्रह्म परमं स्वभावोऽध्यात्ममुच्यते | भूतभावोद्भवकरो विसर्ग: कर्मसंज्ञित: ||

śrī-bhagavān uvāca akṣaraṁ brahma paramaṁ svabhāvo 'dhyātmam ucyate bhūta-bhāva-udbhava-karo visargaḥ karma-saṁjñitaḥ

The Blessed Lord said: The supreme imperishable is Brahman. The Self dwelling in the body is called Adhyatma. The offering that causes the origin of beings is called karma.

Krishna begins answering Arjuna's fundamental questions. 'Aksharam brahma paramam'—the supreme imperishable is Brahman. This is the eternal Absolute, the foundation of all existence that never changes. 'Svabhavo 'dhyatmam ucyate'—the own nature (svabhava) dwelling in the body is called Adhyatma, the Self. This is the eternal consciousness that indwells every being. 'Bhutabhavodbhava-karo visargah karma-samjnitah'—the offering (visarga) that causes (karah) the origin (udbhava) of beings (bhuta-bhava) is called karma. This is the creative action that brings beings into existence. Krishna establishes the framework: Brahman is the eternal foundation, Adhyatma is the Self in the body, and karma is the creative force. This sets up understanding death and rebirth—what's eternal, what's changing, what causes rebirth.