kaṭhopaniṣad - adhyāya 2, vallī 2

The city of eleven gates belongs to the Unborn, whose consciousness is never crooked. By meditating upon Him, one ceases to grieve; being liberated from the bonds of ignorance, one attains final emancipation. This, verily, is That.

He is the Swan dwelling in the light of heaven, the Vasu dwelling in the mid-air, the Priest dwelling by the altar, the Guest dwelling in the house; He dwells in man, He dwells in the superior, He dwells in truth, He dwells in the ether; He is born of the waters, born of the earth, born of truth, born of the mountains; He is the Great Truth.

He leads the Prana (upward breath) upward and impels the Apana (downward breath) inward. That dwarf who sits in the center is worshipped by all the gods.

When this soul, which is lodged in the body, is loosened and slips away from the body, what remains here? This, verily, is That.

No mortal lives by Prana or by Apana; men live by another source on which these two depend.

Come, Gautama, I will declare to you the mysterious, eternal Brahman, and also what becomes of the soul after reaching death.

Some souls enter the womb to take on a body, while others pass into stationary forms, according to their past actions and their inner nature.

That Person who remains awake while all are asleep, shaping one desire after another—that, indeed, is the Pure, that is Brahman, and that alone is called the Immortal. All worlds are contained in Him, and none can transcend Him. This, verily, is That.

As the one fire, entering the world, becomes corresponding in form to every form it burns, so the one inner Self of all living beings becomes corresponding in form to every form, and yet remains outside them all.

As the one air, entering the world, becomes corresponding in form to every form it enters, so the one inner Self of all living beings becomes corresponding in form to every form, and yet remains outside them all.

Just as the sun, the eye of the entire world, remains untainted by the external defects seen by the eyes, so too does the one inner Self of all beings remain untainted by the sorrows of the world, standing apart from them.

He is the one Controller, the inner Self of all beings, who makes His one form manifold. Those wise souls who perceive Him abiding within themselves attain eternal happiness, and none others.

He is the Eternal among the transient, the Consciousness of all conscious beings, who, though one, fulfills the desires of the many. Those wise souls who perceive Him abiding within themselves attain eternal peace, and none others.

They perceive that indescribable, supreme bliss as "This." How, then, can I understand it? Does it shine by itself, or does it cause other things to shine?

The sun does not shine there, nor do the moon and the stars, nor do these lightnings shine, let alone this earthly fire. Everything shines only after that shining One; by His light, all this is illumined.