As is evident, Vedism was only a nature worshipping religion. It never had the slightest notion about a monotheistic Supreme God. In the Vedic days, There were no temples. The Vedic people would pray in the open sitting around a "vedi (altar) " on which fire was lit and this sacrificial ritual was known as jagna. The Rig-Veda has several verses praising Indra, the god of rain and thunder and the king of all gods. Nevertheless, in the Rig-Veda, we never come across words like Bhagwan or Ishwara.

Hindu scholars argue relently trying to establish monotheistic concept in the Vedas by quoting the concepts of Prajapati, Dharr and Tatr. The hymns often cited are purusha-sukta (X-90), nasadiya sukta (X-129) and a few others. These are really post- Christian writings. Monotheistic concepts are either interpolations or were developed late in the Christian era.

Here is the quote on the monotheism in Vedic religion:

"Already the Rigveda, in its youngest books (books 1 and 10) contains evidence for emerging monistic thought. Often quoted are pada 1.164.46c,

and hymns 10.129 and 10.130, dealing with a creator deity, especially verse 10.129.7:

Ékam sát in 1.164.46c means "One Being" or "One Truth". Such concepts received greater emphasis in classical Hinduism, from the time of Adi Shankara at the latest."

All these references are from the youngest of the book which were written duirng the Post Christian period.

These Vedic gods have brought about a question that you may find pertinent. In the tenth book of Rig Veda, hymn 121, you may read: "What God shall we adore . . .?" It is repeated eight times. The answer concludes the poem: "The Creator of Heaven and Earth", also called "Lord of creatures". Evidently this later addition of Rig Veda must have been taken from the early Christian writings. Other interpolations include the ideas of Purusha (the cosmic man), sat (existence), asat (non-existence), kama (desire) as the first seed of mind. These were essentially the concepts expressed in Sankhya philosophy.

Rig Veda does not mention even in passing the Supreme God concept such as, Isvar, Isam, Paramatma, Parmeshwar, Prabhu, Maheshwar, and Bhagavan anywhere. From these, it is evident that the concept of one supreme God did not exist prior to the advent of St.Thomas. It came as a new concept and was adopted by the Indian priestly class to revive their almost lost religious authority.

When and why did monotheism come in India?
[The following detailed study is based on the paper Monotheism in Sonatan Dharma - Hinduism - By Indrajit Ganguli.
Refer also to Ganguli’s book The Gita as It Was: Rediscovering the Original Bhagavadgita by Phulgenda Sinha)]

There is six recognized schools of thought in ancient India. Four of them Sankhya Darshan (Kapila 700 BC, Yoga (Patanjali 400 BC), Nyaya (Buddha 300 BC), Vaisesika, were rational philosophies. Mimansa, and Vedanta were introduced in Upanishads. Next is Charvaka's Lokayatta (Materialism) and his period is dated around 550 B.C. During the period in question, from 5th century B.C. up to 8th century A.D., there was decline in Brahmanism and the new religions of Buddhism and Jainism were well established. Christianity came in with St.Thomas in AD 52 and Islamic invasion took place around 6^th c AD. Vedism coexisted with all these other religions which became powerful and Brahmins lost their position and power.

It was during this period that the original Gita was interpolated and monotheistic concept inserted into what is known as Bhagavad-Gita today. This was done to establish the historical legitimacy of the monotheistic concept. It was for this purpose that the redactors added chapters I and X to the Rig-Veda, reconstructed the epics Ramayana and Mahabharata by identifying Rama and Krishna with The Supreme Being, added several verses to Sankhya Karika to change the original concept, and the concept of Purusha and Prakriti, and added more than 100 verses to the Yoga Sutra of Patanjali to introduce the concept of Isvara (God) and to interpret Yoga as union with God.

The original Gita had only 84 verses and the basic concept was based on Shamkya philosophy. The Bhagavad-Gita has 700 verses and that will mean that 616 verses were interpolated. The interpolated Bhagavad-Gita and other scriptures were corrupted between 800 and 1000 A.D. Research work concerning the interpolation of Gita was done by German scholars such as Richard Garbe, Rudolf Otto, JW Hauer, and others and their findings were later confirmed when copies of the original Gita was discovered in Bali, Indonesia and another one in Farukkabad. Both these versions had 84 verses only. Phulgenda Sinha argues in his book "The Gita as it was" that only the first three chapters of Gita are authenic,and the rest are interpolated around the year 800 in common era. He says that the Gita was written by Vyasa, under the influence of Kapilas samkya philosophy and Patanjalis yoga sutras. After Vyasas first three chapters the Gita seems to have been interpolated by two entirely different authors, one of them monist and the other theist.

Is Hinduism Polytheistic?
http://www.religionfacts.com/hinduism/beliefs/theism.htm

Evidently monotheism in Hinduism is a recent development. Even today the Hindu communities around the world is struggling to make sense out the mess of pantheism, henotheism and idolatry while the big wig in America and Europe are trying to call it monotheism by integrating everything together.

Hinduism is a decidedly theistic religion; the difficulty lies in determining whether it is a polytheistic, pantheistic, or monotheistic. In later Hinduism, the One is simultaneously Many and vice versa. This is a reflection of the Christian Triune God and Hindu avatars retains these characteristics of the early Christian theology.

Monotheism is the worship of One God. Polytheism is the worship many Gods. Monotheism can be given many philosophical shades. In doing so what the Hindu Pandits of the 20^th century has done is to equate Polytheism with Monotheism.

Monotheism = Polytheism.
(see Hinduism : Monotheism and Polytheism Reconciled By Sri Swami Chidananda)

This is how it is done with a twist in logic. The basic assumption is the immanence of God in the universe. God is present in the Sun. So Sun is a God. God is present in the trees. So trees are Gods. In this process of logic everything is God and if you worship the Sun, moon and the stars and rocks and the idols you are still worshipping the One true God. Here is the confusion between part and the whole. God is both immanent and Transcendent. So part cannot be equated with the whole. It will be similar to confusing my shirt with me. There is also the confusion between symbol and reality. The idol, the icon, the pictures and words are all symbols. But if we assume that identity of the symbol with the reality what we get is idol worship. While symbols are powerful means of communication, idols can become means of veiling the truth.

"So is Hinduism polytheistic, pantheistic, or monotheistic? Contributing to the difficulty of answering this question is the fact that Hindus are not nearly as concerned as are western thinkers with such labels and categories. After all, it is a favorite Hindu saying that "The Truth is One, but different sages call it by different names." (A Quote taken from Rig Veda I which was written after the first century AD and this will be important to see how this idea came about.) But when Hindus do define their religion in these terms, usually for the benefit of curious westerners, they tend to do so in terms of monotheism and pantheism:

Only a Smartha, or follower of the Advaita philosophy, would have no problem worshiping every imaginable deity with equal veneration; he views these different deities as being manifestations of the same God. You don’t need to call it God, because that is the only reality. Everything else is an illusion or dream of that conscious being. In the twentieth century Hindu religion in the west is identified with the Smartha.

Other Hindu sects, such as Vaishnavism and Shaivism conform more closely to a Western understanding of what a monotheistic faith is. Vaishnavites considers Vishnu as being the one and only true God. But there is a blurring of the oneness with the concept of avatars – the incarnations. According to Vaishnava doctrine, there are two type of avatars – Svarupavatars (Purna avatars of Full Form of Vishnu) and Amsa Rupa avatars ( avatars of partial form). In the full avatars, the godhead himself incarnates while in the partial avatars only certain powers are manifested through certain creatures and persons. The problem is that there are large number of Full incarnations and an infinite number of partial incarnations of Vishnu

According to the Puranas countless numbers of avatars descend into our universe.

O brahmanas, the incarnations of the Lord are innumerable, like rivulets flowing from inexhaustible sources of water.

Dasavatara as given in Garuda Purana

1. Matsya, the fish
2. Kurma, the tortoise
3. Varaha, the boar
4. Narasimha, the half-man/half-lion
5. Vamana, the dwarf
6. Parashurama, Rama with the axe
7. Rama.
8. Krishna
9. Buddha some versions of the list contain no reference to Buddha instead we have Balarama according to the Bhagavata Purana He is also counted as an avatar of Vishnu by the majority of Vaishnava movements and is included as the ninth Dasavatara.
10. Kalki to come yet.

Theologically within Vaishnavism the many avatars have been categorised into a number of different types depending on their specific personality and role as described in scripture. Not all are recognised as 'full' or 'direct' incarnations of Vishnu. Some avatars are believed to be souls blessed with certain abilities of 'divine origin', although being a jiva themselves.

Bhagavata purana lists over 22 such avatars. . It is still considered monotheistic since if you worship the partial incarnation you are woshipping the Fullness. After all you can worship a part and still be worshipping the full.

A more realistic monotheism very similar to Christianity is found in Saivism. Siva has no incarnation. Originally there were the trinity in the godhead – Appan, Amma and Makan – Father, Mother and Son. Saivites believe God transcends form, and devotees often worship Siva in the form of a lingam (Formless Form), symbolizing all universe.

Later other progenies of Siva were added which includes Mani and Ayyappa.

Because of these exclusivism, Saivites and Vaishanavites were constantly at war with each other.

Great number of temples in south India were built during the thousand years between 600 and 1600 A.D. Buddhism had great influence in the down south, especially part of the present Tamil Nad and Kerala. Saivism (Shiva Siddhanta) was more popular in the Dravidian South while Vaishnavism was more popular in the Aryan North. There are historical evidence for intense rivalry between the Saivites and the Vaishnavites. It is probable that the dramatization of Sabarimala Ayyappa is a compromise between Buddha, Siva and Vishnu worshippers. The name, Dharma Shastha and the prayer song "Swamiye Saranam" are strong indications of the influence of Buddhism. The Vratham, Pilgrimage and associated rituals points to influence of Advaita and Dwaita sects.

1. Semitic model (Judaism & Islam) :
   God is One Person and there is no other beside Him. God is the creator of both good and evil. Every creation is outside of God and is controlled by Him.
   
2. Greek model :
   God is not the name of A Person but a common noun. Thus Plato speaks of "the gods (hoi theoi), or "the god (ho theos)", in some cases of "god", but then in the same way we would talk of "man", using the word as a generic name. He also speaks of "the divine (to theion)".
   
   Aristotle concluded that "being" primarily refers to the Unmoved Movers, and assigned one of these to each movement in the heavens
   
3. Vedic Model
   In popular Indo-European (Greek and Vedic) religions the deities are anthropomorphic. This is Polytheism, where there is no God who is absolutely supreme or above all others. These beings are in constant interactions and creates their own hierarchy by virtue of the powers they have and powers they acquire and create. This includes Nature gods, spirits and beings that depend on matter and non-matter. These nature gods can be controlled by sacrifices and presents. They do not define good or evil.
   
4. Buddhist Jain Model:
   There are very many beings in the cosmos in different levels of existence and energies. There are both beings and non beings – Purusha and Prakriti. They are in constant flux driven by the laws of existence which are immutable
   
5. Christian model :
   Christians believe that the one God is Triune (the Holy Trinity). However, this is not a denial of monotheism but an affirmation of the complexity of the Divine Being. In human terms God is a Community which thinks and act in unison by nature. This community of God is an Organism. This is a recognition that God cannot be thought of in terms of the human dimensions. There are dimensions beyond our comprehension which are to be taken into consideration. The Eastern Christian Churches proposes the unity of God in that even the creation itself is within the dimension of divine, so that all creations are part of the divine. But part is not whole in that the creation in itself is not God. Thus God is both immanent and Transcendant in creation.
   
   The various sects of the Hindus has similar theology which are monistic as well as henotheistic. Saivism and Vaishanvism are examples of this. Vashnavism later expanded an open definition which removed the parameters of definition as to what is incarnation thus moved towards polytheism. The Smarta model removed all the boundaries: Self, The All, is One sheer Being present in every part of creation in terms of a manifold of impersonal & personal Divine Self-manifestations. Hence every part of the cosmos is divine in its fullness. It was Shankaracharya in AD 800 who brought this interpretation to justify worship of all different gods. He said that any of the different Hindu gods could be worshipped, since all are different manifestations of Brahman. In fact one can worship anything since they are all aspects of god.
   

1. Immanentism without Tanscendism : God and creation are the same. There is no Divine essence outside creation, for Divine essence equals Divine existence.
2. Transcendentism without Immanentism: God and creation radically differ. There are two realities Prakriti (Creation) and Purusha (Creator)
3. God Immanent and Transcendant : God is immanent in creation, but God is more than the creation. God existed before the creation. There is a distinction between essence and existence. Creation is a manifestation of God's Power.