The idea that part of God (or the Universal World Soul -Soul a-atman or Brahman) resides in the human soul as Jiva-atman,was first proposed by the Upanishads. Later religions considered this concept blasphemous, as it was akin to man proclaiming himself as God. But the Upanishads teach this concept as a non-denominational phenomenon, for the sake of spiritual uplift and Self-Realization. They do not claim one religion superior to another, and the philosophy of Upanishads goes beyond religious beliefs and faiths. In fact, man is encouraged to follow the religion he is born into rather than change to another faith. 

The spiritual uplift can be achieved with gathering of knowledge, the so-called Atma-vidya. The experience of Self-Realization is purely individual and intuitive, perhaps with the help of a guru to guide. Otherwise, the path is solitary, without any communal gathering, worship or ceremony. The essence of Upanishads caught the attention of those who were responsible for the renaissance of the Hindu religion in the 19th century like Vivekananda and Paramahamsa. 

It was realized that one lifetime was not enough to gather this knowledge and hence the concept of reincarnation (Punar-janma) was born. But, if what is learnt in one lifetime is forgotten and one has to relearn again in the next life, any numbers of lifetimes are not enough. Thus the karma concept took shape. If one's deeds are etched indelibly on one's soul (Sanchita karma), and then transported from birth to birth, the cumulative knowledge over many rebirths would suffice to attain the salvation that the soul craves for. The ultimate goal of all human beings is to shed the bodies, like changing soiled clothes, and rejoin their souls with that of God (liberation of the soul or moksha). Thus the soul desires to be transcendent and reach its origins.

The notion of dispensable body and the eternal soul is unique to Upanishads. Prior to this thought was proposed by the Upanishads, a Vedic Hindu's aim was to advance himself and reach immortality by reaching the ranks of the heavenly beings, and live in a higher world in bliss. There are many stories in the puranas, wherein powerful men through meditation reached such a stage and were able to challenge Indra. Indra had to appeal to higher gods to come to their rescue. Upanishads taught that by paying attention to the soul within that resembled God, every human being could attain bliss. 

The philosophy of three main branches of Sanatana Dharma, namely Advaita, Vishishtadvaita and Dvaita may vary slightly but the central core of all three concepts is the same; the human soul desires to be joined with, or wants to be close to the World Soul. Release from the cycle of repeated births and consequently the suffering of the soul is the primary goal. Life of virtue, sacrifice, worship and service of humanity will hasten the release of the soul from the earthly chores and sorrow.

Progression of Worship

How did we get here from the original Aryan migration to the Indus Valley more than four thousand years ago? When they first arrived (about 2000B.C.), to their surprise, they found a very well organized society (pre-Aryans), with their cities, roads, drainage system, and water tanks for communal bathing. Nomadic Aryans quickly assimilated into this society and both societies seemed to have mutually benefited. Aryans did have superior weapons and two wheeled horse-driven chariots, which were faster than the indigenous carts pulled by bullocks. Though they dominated the local population and called them dasas (servants, slaves), there seems to have been fair relationship between the two groups. There were no wars fought or any signs of brutality in the excavations of Harappa and Mohenjo Daro. 

When the Aryans came to the Inuds valley of seven rivers (Sapta Sindhu) over many centuries, they brought with them the hymns of Rig Veda (samhita). These were oral traditions that had been passed from generation to generation. They had been formatted in such a way that it was easy to memorize without looking at written words. The Aryans found a strong practice of worship among the pre-Aryan tribes, who had been living in those regions for at least one thousand years before their arrival. Phallic symbols of male virility in the form of lingas (similar to ones found today), and a mother goddess, a symbol of fertility were the deities worshipped by these pre-Aryans. Aryans on the other hand had no idols and worshipped nature, as human forms that resided in the heavens. Indra was their main benefactor and object of worship. Warrior Indra was admired for his bravery rather than for his benevolence. About half of the hymns of Rig Veda are praises for Indra. Agni was the next and was important in the sacrifices and was considered as a messenger, carrying the messages to the heavens, as the flames of the sacrificial fires ascended upwards. Other gods like Varuna (God of nature and moral order), Vayu (wind), and Ushas (dawn), Prithvi (earth) and many more were also important. Vishnu also was a warrior God and his ten avatars had not yet been conceptualized. 

The subdued class of the pre-Aryan tribes had a different mode of worship. It resembled the current form of worship that Hindus practice today in the temples and in their homes. Offerings of food and flowers, milk, oils and red ochre (kum-kum) were perhaps the daily ritual. Some of the fierce forms of mother goddess may have been appeased with animal sacrifices, just as the practices of offering of animals continue today in the worship of Kali. The Aryans (perhaps the Brahmin sect) adopted and incorporated this form of worship of idols and added chanting of Vedic mantras during worship of idols. Ironically, thousands of years later, it is the pre-Aryan form of prayer ritual, mostly unchanged, that is prevalent in modern Hinduism. The Aryan sacrificial ritual has been reduced to the ritual of performance of havan orhoma, only for special occasions. The dominated servant class of dasas had prevailed after all! Shiva and the mother goddess (Shakti), the pre- Aryan deities are still preserved. Indra and Agni, though revered have lost their 'God' status. Brhama and Shiva were added to the Hindu pantheon much later by Aryans (who by now hardly resembled the original nomadic Aryan tribes that had come to India through the Northwestern mountain ranges, to dominate a well-established society).  

Floods and famine along the legendary Saraswati River drove the people eastward to the Gangetic planes, were they set up a flourishing society. The Vedas had been slowly expanded to include the massive Brahmanas, the instructions of sacrificial rituals. 

Originally only three Vedas were recognized. Atharva Veda was not considered as Shruti literature until much later. It is thought that the Atharva Veda that deals with the occult including tantras was a product of the pre-Aryan thought process. Hence it could have been as old as Rig Veda. Later Atharva Veda became the fourth and one of the most important Vedas that gave guidance to most people living their daily ordinary lives. They seem to contain many popular beliefs and customs, perhaps as practiced by the non-Aryan locals, and were later accepted by the aristocracy and the priestly class. Esoteric knowledge dealing with Yantra, Tantra and Mantra are detailed. The Atharva Veda also contains the Ayur Veda, which perhaps was the practice of medicine that the pre-Aryans practiced before the Aryans arrived. The later Upanishads are attached to Atharva Veda.

The philosophic literature like the Darshanas (e.g. Nyaya, Sankhya, Yoga and Vedanta) and Ithihasas (Ramayana and Mahabharata) were written. The dates of the latter are not certain but other literature from prior to Buddha period (6th century B.C.) did not allude to them. The laws of Manu (Manuva Shastra) became a manuscript that dictated moral and social codes of conduct. Verses of Bhagavad Gita were accumulated, perhaps over a period of many decades or centuries. Kshatriyas, the ruling class, and the priestly class of Brahmins began to exert pressure on the society and the caste system became more systematized. The study of the massive Vedas became taboo to the lower castes and women. The subdued castes naturally dissented and slowly other opinions and thought process developed. Philosophers started questioning the meaning of the very existence of man. Sages in their ashrams taught the great Upanishads. The concept of parama-atman (World Soul) that resides in humans as jiva-atman was born. The teachings of Upanishads encouraged many people of lower castes to question the authority of higher classes. The non-denominational philosophy of the Upanishads gave hope to many ordinary people. Atheistic religions like Buddhism and Jainism, Ajivikas and Charvakas took hold. The Brahmin class, feeling threatened by the new wave of thinking that could erode their power, adopted Upanishads that eventually became the last part of Vedas. Over many centuries newer Upanishads were added. Earlier prose Upanishads were written 800 '500 B.C. and the later verse Upanishads were from 500 ' 200 B.C. The philosophy of the different Upanishads summarized in Vedanta sutra (also called Brahma sutra) came to be known as Vedanta (end of Vedas). 

As Buddhism spread and took a firm foothold after Ashoka's rule, Sanatana Dharma transformed itself from the sacrificial worship to the bhakti form of worship. Aryans had forgotten their original Gods and adopted the pre-Aryan deities. Abodes to the Trinity of Gods ' Brhama, Vishnu and Shiva - were built and temple worship became common. By the fourth century A.D. (Gupta period) a new form of Sanatana Dharma had emerged. Worship of idols as symbols of God became common. A pantheon of new Gods was added, though the basic idea of Upanishads - of monism - was preserved. The various Gods were referred to as manifestations of a single God - this was the Nirguna Brahman of the Upanishads - formless, characterless, one without attributes, but all pervasive and omnipresent. For the sake of worship, Brahman was given form and character, as other names and temples were built for these Gods. Five hundred years later a child prodigy within a short life span of 32 years, transformed religious and spiritual India. Shankaracharya, synthesized the Sanatana Dharma again and organized in such a way that all the pantheon of gods and fractious groups could be brought under a single religious sect, glued together by the philosophy of the Upanishads. Like Buddha, Shankara also viewed the world in two planes ' one an illusory (maya) and another higher plane. God played the ongoing struggle of the daily chores of life like a puppeteer playing the strings attached to the puppets (lila). Two more Acharyas -Ramanuja and Madhva - who proposed slightly different approaches followed him, without deviating from the teachings of the Upanishads. Since about the fourteenth century there has been a damper in the progress of literature and commentaries to Sanatana Dharma. First by the aggressive religion of Islam and later by the Anglicization of India by the British, as its rulers, denied the progression of philosophical thought in India. However, in the 19th century, a renaissance of the religion took place by such men as Ramakrishna Paramahamsa, Rajaram Mohan Roy, Dayanand Saraswati and Vivekananda.

For all practical purposes, Hindu worship today follows the Gods first worshipped more than 4500 years ago by the pre-Aryans. The worship has been refined by the wisdom of the Vedic mantras and the philosophy of the Upanishads. But the transformation of the religion is far from over and the ever-evolving Sanatana Dharma seems to have no limits or boundaries.