Mandala Brahmana, the 28th of the 108 Upanishads, is attached to the Sukla Yajur Veda. In it a sage reaches the sphere of the Sun and learns about the light that exists within man, the core of the seeker himself.
The great muni Yajnavalkya went to Adityaloka, the Sun's world and from the Purusha of the Sun he learned thus.
The body has five stains: passion, anger, unrest, fear and sleep. The removal of these can be effected respectively by abstaining from sankalpa (intention) and by practicing forgiveness, moderate food, carefulness and the spiritual sight of tattvas. In order to cross the ocean of samsara, where sleep and fear are the serpents, injury is the waves, desire for sensations is the whirlpool and family is the mire, one should adhere to the subtle path and look for the mystical Taraka.
Taraka is Brahman when nested in the middle of the two eyebrows, having the nature of the spiritual effulgence of satchitananda. Sushumna, the channel leading to it, has the radiance of the Sun. In this channel's center, the kundalini shines like millions of lightning bolts and yet is subtle as the thread in the lotus stalk. Tamas is destroyed there. Through seeing it, all sins are destroyed.
When the two ears are closed by the tips of the forefingers, a phutkara (booming) sound is heard. When the mind is fixed on it, a blue light is seen between the eyes and also in the heart. When one looks at the external space, moving the eyes and sees streaks of light at the corners of his eyes, then his vision can be made steady. When one sees jyotis (spiritual light) above his head, 12 digits in length, then he attains the state of nectar and sees the variegated colors of the morning as if the sun, the moon and the fire had joined together in the akasha. Then the yogi comes to have the nature of those lights. Through practice, he becomes one with akasha, devoid of all gunas and peculiarities.
At first, akasha, with its shining stars, becomes to him Para-akasha and he becomes one with Para-akasha. Then he becomes one with Maha-akasha, resplendent as a deluge of fire. Then he merges into Tattva-akasha, lighted with the highest conceivable brightness. Then he becomes one with Surya-akasha, brightened by millions of suns. By practising thus, he becomes one with that.
This is the great science which is concealed in all the tantras. When this is known, one does not stay in samsara.
Then Yajnavalkya asked the Purusha in the sphere of the Sun: "O Lord, antarlakshya (inner sight) has been described many times, but it has never been understood by me. Pray describe it to me."
The Purusha of the Sun replied: "It is the source of the five elements. In its midst, the tattvas are manifested. It is very hidden. It can be known only by one who has got into the boat of jnana. Above the inner sight is the sphere of the sun; in its midst is the light of the nectary moon. It has the brightness of shukla (white light), like a ray of lightning. Its lakshya (aim) is the tip of the nose. When this is practiced, a deep darkness is seen at the root of the palate. By practising thus, a jyoti (light) of the form of an endless sphere emerges. This is Brahman as satchitananda. When the mind is absorbed in bliss thus naturally produced, then the kechari mudra takes place.
"The following are the signs: first light is seen like a faraway star; then a dazzling diamond; then the sphere of full moon; then the sphere of the brightness of nine gems; then the sphere of the midday sun; all these are seen in order.
"As there is no rising or setting of the eternal sun of Chit (awareness), in the heart of a man who knows thus, he has no karma to perform. Rising above day and night through the annihilation of sound and time he becomes one with Brahman. Not being troubled by any thoughts, he is the jnani.
"When the triputi (knower, knowing and knowledge) are thus dispelled, he becomes the jyoti without bhava (existence) or abhava (nonexistence), full and motionless, like the ocean without the tides or like the lamp without the wind. All that is not other than the Self into which the whole universe is absorbed, as the universe is a delusion of the mind and is therefore not different from it.
He who knows Brahman and thus enjoys this bliss, which is eternal and has dawned on him, that man becomes one with Brahman."
K. Narayanasvami Aiyar published this translation of Mandalabrahmana Upanishad (slightly edited here) in 1914 along with the Adyar Library as part of his book, Thirty Minor Upanishads. The translation had previously appeared in the monthly journal, The Theosophist. He collaborated on the work with Sundara Sastri.
The Vedas are the divinely revealed and most revered scriptures, shruti, of Hinduism, likened to the Torah (1200 bce), Bible New Testament (100 ce), Koran (630 ce) or Zend Avesta (600 bce). Four in number, Rig, Yajur, Sama and Atharva, the Vedas include over 100,000 verses. Oldest portions may date back as far as 6500 bce.