tattvaṁ yaj jñānam advayam
bhagavān iti śabdyate
Lord Krishna (Sri Bhagwan or Supreme (Para) Brahman) speaks about Himself and his other two aspects i.e Brahman and Parmatma form in the Bhagavad-gita as follows.
Lord Krishna says in Bg 14.27
brahmaṇo hi pratiṣṭhāham
I am the basis of the impersonal Brahman
Brahman is the bodily effulgence of Supreme Person just like Sun and its rays.
— I worship Govinda, the primeval Lord, whose effulgence is the source of the nondifferentiated Brahman mentioned in the Upaniṣads, being differentiated from the infinity of glories of the mundane universe appears as the indivisible, infinite, limitless, truth.
It is also explained in Sri Ishopanishad:
pūṣann ekarṣe yama sūrya prājāpatya
vyūha raśmīn samūha
tejo yat te rūpaṁ kalyāṇa-tamaṁ
tat te paśyāmi yo ‘sāv asau puruṣaḥ so ‘ham asmi
— O maintainer; – — the primeval philosopher; — the regulating principle; — the destination of the sūris (great devotees); — the well-wisher of the prajāpatis (progenitors of mankind); — kindly remove; — the rays; — kindly withdraw; — effulgence; — so that; — Your; — form; – — most auspicious; — that; — Your; — I may see; — one who is; — like the sun; — that; — Personality of Godhead; — myself; — I; — am.
O my Lord, O primeval philosopher, maintainer of the universe, O regulating principle, destination of the pure devotees, well-wisher of the progenitors of mankind, please remove the effulgence of Your transcendental rays so that I can see Your form of bliss. You are the eternal Supreme Personality of Godhead, like unto the sun, as am I.
The other two aspects are Parmatma and Himself (Krishna or Supreme Person the primary aspect).
Parmatma or Supersoul :
I am in everyone’s heart as the Supersoul. As soon as one desires to worship some demigod, I make his faith steady so that he can devote himself to that particular deity.
Kaṭha Upaniṣad (1.2.20) :
aṇor aṇīyān mahato mahīyān
ātmāsya jantor nihito guhāyām
tam akratuḥ paśyati vīta-śoko
dhātuḥ prasādān mahimānam ātmanaḥ
“Both the Supersoul [Paramātmā] and the atomic soul [ jīvātmā] are situated on the same tree of the body within the same heart of the living being, and only one who has become free from all material desires as well as lamentations can, by the grace of the Supreme, understand the glories of the soul.”
Lord Krishna expands himself into unlimited forms and resides in each and every living entity’s heart with the soul of that body.
Sri Bhagavan or Supreme person:
— O conqueror of wealth, there is no truth superior to Me. Everything rests upon Me, as pearls are strung on a thread.
— O son of Pṛthā, know that I am the original seed of all existences, the intelligence of the intelligent, and the prowess of all powerful men.
— Know that all states of being – be they of goodness, passion or ignorance – are manifested by My energy. I am, in one sense, everything, but I am independent. I am not under the modes of material nature, for they, on the contrary, are within Me.
— Deluded by the three modes [goodness, passion and ignorance], the whole world does not know Me, who am above the modes and inexhaustible.
— After many births and deaths, he who is actually in knowledge surrenders unto Me, knowing Me to be the cause of all causes and all that is. Such a great soul is very rare.
— Men of small intelligence worship the demigods, and their fruits are limited and temporary. Those who worship the demigods go to the planets of the demigods, but My devotees ultimately reach My supreme planet.
— There are two classes of beings, the fallible and the infallible. In the material world every living entity is fallible, and in the spiritual world every living entity is called infallible.
— Besides these two, there is the greatest living personality, the Supreme Soul, the imperishable Lord Himself, who has entered the three worlds and is maintaining them.
— Because I am transcendental, beyond both the fallible and the infallible, and because I am the greatest, I am celebrated both in the world and in the Vedas as that Supreme Person.