śrīmadbhagavadgītā puruśottamayogaḥ
Bg 15.18
yasmāt kṣaram atīto ’ham akṣarād api cottamaḥ
ato ’smi loke vede ca prathitaḥ puruṣottamaḥ
Bg 15.19
yo mām evam asammūḍho jānāti puruṣottamam
sa sarva-vid bhajati māṁ sarva-bhāvena bhāratā
yasmāt aham atītaḥ kṣaram - Since I (=Bhagavan Krishna) am beyond the persihable material universe,
ca api uttamaḥ akṣarāt - and also excelling the imperishable consciousness/soul elements of the universe,
ato ’smi prathitaḥ puruṣottamaḥ loke vede ca -therefore am I declared as the Supreme Personality in the world and also in the scriptures(=Vedas).
bhāratā - Oh Arjuna,
yo asammūḍho jānāti mām evam puruṣottamam - the one who is not confused and knows me thus, as the Supreme Personality,
saḥ sarvavit bhajati māṁ sarva-bhāvena - that man is all-knowing, and worships me through his entire being.
These two shlokas occur in the fifteenth chapter of the Bhagavadgita. In the entire Gita, this chapter has been clearly called as a "Shastra" (and no other chapter!) This means that this chapter represents the core message of God.
In this chapter, most eloquent in imagery and captivating in poetry, God conveys the meaning of this universe, and how He empowers everything. He also states that He is beyond material existence and individual souls which carry consciousness and impressions from birth to birth. Thus he is the supreme Lord and called God.
(photo taken in Kota Kinabalu, Malaysia, 15 Feb.2006).