अहमात्मा गुडाकेश सर्वभूताशयस्थितः ।
अहमादिश्च मध्यं च भूतानामन्त एव च ।। १०.२० ।।

aham ātmā guḍākeśa sarva-bhūtāśaya-sthitaḥ |
aham-ādiś-ca madhyaṁ ca bhūtānām-anta eva ca || 10.20 ||

Audio-BG-10.20-Part-1

Audio-BG-10.20-Part-2

He first points out that the Supreme reigns in the heart of everything, be it small or big. The mystery of creation is always a work from within. The wonder-worker is inner, not outer. Every form of existence is a resultant of its own inner majesty, grandeur. Any birth anywhere is but a growth, an expression. And it is the display of the power and glory, lurking within that has come to express visibly.

Seated in the core of the very ideational process in every being, O Arjuna, the Supreme reigns as the beginning, middle and end of all existences.

To trace the Supreme or think of its glory or splendour, one has to be focused within, not without. Such exclusive inner focus is the core of true spiritual effort and vision.