The Christians use it to denote the second person of the Trinity. The ancients in the West inherited this concept from their ancestors who, thousands of years before the Christian era, had come to acquire a great love and adoration for Surya which they regarded as the be-all and the end-all of all human endeavors in their search for the mighty power of God, and as a visible representation to this earth. They carried this notion along with them wherever they went, Eastward or West- ward, and composed hymns and chanted psalms in praise of the glorious orb, the source of all life on this solar planet. Those who settled in Iran ( Persia) and came subsequently to be known as Parsees, still worship the great deity in yet another form-fire-which they keep burning all the time in their temples as symbolic of the sacred flame that burnt in the human heart and always sprang heavenward. Ratu Zoroaster , the Iranian prophet of life and light, sang in loving and living faith of the greatness of the God of Light and taught the people to do so.

Agni or fire was a hidden secret with the gods, who guarded this mysterious power very jealously. It was, as the Greek legend goes, stolen by Prometheus and given to man, for which Jupiter, the father god, bound him to eternal torture. In Chapter VI of the Chhandogya Upanishad, it is said to be "the prime element whose creation made possible that of other elements, water, earth," etc.

The second branch of the Aryans which turned eastward into the Indo-Gangetic plain also referred lovingly to Aditya; and we have hymns in the Vedas addressed to Hiranyagarbha, Savitar and Usha, all of which stand for the One life-sustaining power, the Sun. The worshipful Masters of the Vedic age were, one and all, admirers of the purifying and healing attributes of the Sun-god, and so no wonder that we see many hymns in the Vedic literature deifying the sun. In Book X, 121, we find:  

In the beginning rose Hiranyagarbha, born as the only lord of all created beings ;

He fixed and holdeth up this earth and heaven;

What god shall we adore with our oblation? ...

What time the mighty water came, containing the Universal germ, producing Agni,

Thence sprang the God's One Spirit into being:

What god shall ule adore with our oblation?  

In another hymn, he is referred to as "the self-radiant wise Aditya. ;In Book I, 113, we have a hymn to Dawn and in it occur, inter alia, the following lines :

This light is come, amid all lights the fairest; born is the brilliant, far: extending brightness.

Night, sent away for Savitar's uprising, hath yielded up a birthplace, for the morning. ..

Arise! the. breath, the life, again hath reached us: darkness hath passed away, and light approacheth.

She for the sun hath left a path to travel; we have arrived where men prolong existence.

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All this could be taken on the literal plane as little more than Nature-worship, an adoration of the sun, understandable among a people dependent upon agriculture for their existence. But ancient Indian literature has an elusive quality. It seems to teach us at one level, and when we have adjusted ourselves to it, it suddenly shifts us to another. He who can follow its subtleties finds in it a richness rarely to be met elsewhere . There is multiplicity of meanings, ranging from the physical to the cosmic and the spiritual, and from the literal to the symbolic and esoteric, which challenge us at multiple levels of experience and offer us worthwhile rewards. Thus, when we begin studying these frequent references to the sun, we begin to see that the "sun" referred to is not always the center of our physical Universe, which we initially took it to be. Thus,in the Isha Upanishad, we are told:

The door of the True One is covered with a golden disk.

Open that, O Pushan, that we may see the nature of the True One.

After recounting such statements, when we read of Brahman or the Supreme One, as being Jyotisvat, full of light, and Prakashvat, endowed with splendor, we begin to discover in such terms an esoteric significance we earlier overlooked. This comes to a head when we read the Gayatri , the tenth mantra of the sixteenth sutra in the third mandala of the Rig Veda:  

Muttering the sacred syllable ," Aum" rise above the three regions,

And turn thy attention to the All-Absorbing Sun within.

Accepting its influence be thou absorbed in the Sun, And it shall in its own likeness make thee All Luminous.

This mantra is considered the most sacred, the mool mantra among the Vedic texts, and is taught for recitation among Hindus from an early age. Here, the inner spiritual meaning of the "Sun" becomes abundantly clear. The object of veneration is not that which provides us with light in the outside world but it is a principle that transcends the three planes of existence, the physical, the astral and the causal, and is the source of inner illumination.

This principle is referred to as Aum, a term whose three letters suggest the three phases of human experience: "A" referring to the waking state (jagrat), ".U" the dream state (swapna) and "M" the deep sleep state ( sushupti ) .

The ultimate reality includes all three planes, and the three phases of human experience, yet goes beyond them. The silence that follows each recitation of the word Aum suggests the state of Turiya or Absolute Being, which is the indescribable source and end of everything. It is the Brahman the  All-transcending One,whose prime attribute is effulgence, but who is in himself even beyond this effulgence. Hence the mantra in its original Rig Veda form has another line added to it, which is given out only to sanyasins and chosen disciples-Paro Raj-asal Savad Aum: He who transcends the effulgence is this Aum.

The Gayatri  not only clarifies the routine implications of the references to the sun, abundant in the Vedas, but it also highlights another recurring theme in Hindu thought. Its wide imagery and popularity bring us to the question of mantras and their place in Indian religious practice. The mantras or verbal formulae in Sanskrit verse or prose are classified into two types: those that are meant simply for recitation and need not be understood, and those that are divine invocations, whose import must be known in order to enable the devotee to keep his attention focused on the divine object. The various mantras each have their individual benefits. There are those whose mastery or siddhi gives one contact with magical powers of a lower order (tamsic) ; there are others that bestow strength and courage and power ( rajsic ) ; and finally those whose sole object is sportual  upliftment . Among the last as we have already seen, the Gayatri is the most venerated.

The mode of mantras, since time immemorial, stresses the spiritual importance of Sound. If the chanting of certain verbal formulae brings magical potential or assists spiritual advancement, then there must be latent in Sound itself an esoteric power. "This is why Vak Devi, the goddess of speech, was held in high esteem. Each word has its unique character and place, but of all words Aum is the most sacred. We have already examined some of its symbolic meanings. To these we may add still others. It is not only a term that connotes the qualities of the Absolute Brahman, but one that also denotes Brahman Himself. In the Rig Veda, we have:

Prajapati vai idam agref aseet

Tasya vag dvitya aseet,

Vag vai parmam Brahma.

("In the beginning was Prajapati, the Brahman, with whom was the Word and the Word was verily the Supreme Brahman." ) This text remarkably parallels the opening of the Gospel according to St. John:

In the beginning was the Word, and the Word was with God and the Word was God.

Thus Aum becomes Brahman as manifesting Itself in the Word, and in the Taittriya Upanishad, It is referred to as the "Sheath of Brahman," as something which takes Its life from Brahman and contains Him. This aspect is made even clearer in the Sam Veda:

Brahman is at once Shabd and Ashabd both, And Brahman alone vibrates in space.

In other words, the Absolute One is not only inner effulgence but also beyond it, as suggested in the Gayatri. He is with the Word, the Shabd or Aum, yet beyond It. Both Sound and Light are in fact referred to as His prime manifestations. The Gayatri recommends that while concentrating on the Divine Word Aum, we fix our attention upon the inner Sun, while in the Chhandogya Upanishad, we are told that Naad , or the divine music, springs from the Universal Sun ( of Brahmand) , a secret that was given by Angris Rishi to Krishna, the darling son of Devki .It was this mystic insight to be found in the srutis, the scriptures revealed through inner hearing, that led to the development of what came to be called the Sphota-vada or the philosophy of the Word. The teachers of this path preached that the Absolute was Wordless, imageless, indescribable and   unconditioned. When He came into manifestation, He projected Himself as the Sphota or the Word, radiant with Light and vibrating with indescribable Music. The seeker wishing to transcend the relative plane to the Eternal and Unchanging must contact the Sphota or the Word Power through which he can rise to the Brahman who is beyond Shabd or Sphota. The Path of God-realization is certainly not easy. It is difficult to have access to, difficult to cognize, difficult to abide by and difficult to cross ; yet it is the only possible Way , for one who is true to his Guru and His cause.

Such indeed are the truths that were taught and practiced by the forest sages of ancient India. But how much of them has survived since then? For the most part we find rituals such as the blowing of conches, ringing of bells, waving of lights, and the worship of the sun. These bear testimony to the mysteries within, but how few are conscious of their real significance? In spite of Lord Krishna's powerful and lasting influence which brought the best of the Vedantic teachings to the heart of the common man, religion in India as elsewhere has tended to degenerate into mere caste and ceremony. The light and music outside are worshiped, but the flaming and sounding Word within, toward which they point, goes unheeded; "the light crieth in the darkness and the darkness comprehendeth it not."