Monotheism is defined as the belief in only one God and polytheism is defined as belief in many Gods.+

Theism is in traditional sense; it is the belief in at least one God. Monotheism is defined as the belief in only one God and polytheism is defined as belief in many Gods.

Some organized religions follow monotheism where God is supreme and none except him. These God-centric faiths follow a particular code of conduct that the ‘believer’ has to follow without questioning. He cannot question those rules, the life of the Sage or the ultimate God. The individualized Gods God is isolated from nature and everything is GOD’s. Thus,  an element of attachment to a name and gender, obstruction to free thinking and free will can be seen in all belief system.

History speaks that in the past those who questioned the validity of this religious authority were exiled, killed or termed as irreligious and condemned.

Theism, in this specific sense, conceives of God as personal, present and active in the governance and organization of the universe.

The Bhagavad Gita: ~ Brahmano hi pratisthaham ~ Brahman (God) is considered the all-pervading consciousness, which is the basis of all the animate and inanimate entities and material. (14.27).

When Bhagavad Gita says, God is considered the all-pervading consciousness which is the basis of all the animate and inanimate entities and material then nothing has to be accepted as God other than consciousness. 

Lord Krishna Says Ch ~V: ~ “Those who know the ‘Self’  in truth.". The last two words (tattvataha) are usually ignored by pundits, but they make all the difference between the ordinary concept of God and the truth about God.

The dualistic worship of "God” is only for the ignorant populace. The God in truth is only Atman, the innermost ‘Self’.   In reality, there is no dualities, no differentiation. Only Atman exists.

The Vedas confirms God is Atman (Spirit), the ‘Self’.

Rig Veda: ~ The Atman is the cause; Atman is the support of all that exists in this universe. May ye never turn away from the Atman the innermost ‘Self’. May ye never accept another God in place of the Atman nor worship other than the Atman?" (10:48, 5)

Rig-Veda 1-164-46 and Y.V 32-1 clearly mention that God is “One”.

Rig Veda says God is ‘ONE’ and God is Atman, then why believe and worship in place of real God.

Brihad Upanishad: ~ “If you think there is another entity, whether man or God there is no truth."

When Upanishad itself says: ~   Sarvam khalvidam brahma ~ all this (universe) is verily Brahman. By following back all of the relative appearances in the world, we eventually return to that from which it is all manifest – the non-dual reality (Chandogya Upanishad). 

It proves the Vedic Gods are not with the Gods with attributes because the Vedic God is spiritual God because the Vedas consider God as the Supreme Spirit which is Atman.

That is what Yajurveda says:~  not to worship the things which are part of the falsehood. 

Translation 1.

They enter darkness, those who worship natural things (for example air, water, sun, moon, animals, fire, stone, etc).

They sink deeper in darkness those who worship sambhuti. (Sambhuti means created things, for example, table, chair, idol, etc.) (Yajurved 40:9)

Translation 2.

"Deep into the shade of blinding gloom fall asambhuti's worshippers. They sink to darkness deeper yet who on sambhuti are intent." (Yajurveda Samhita by Ralph T. H. Giffith pg 538)

Translation 3.

"They are enveloped in darkness, in other words, are steeped in ignorance and sunk in the greatest depths of misery who worship the uncreated, eternal prakrti -- the material cause of the world -- in place of the All-pervading God, But those who worship visible things born of the prakrti, such as the earth, trees, bodies (human and the like) in place of God are enveloped in still greater darkness, in other words, they are extremely foolish, fall into an awful hell of pain and sorrow, and suffer terribly for a long time." (Yajur Veda 40:9.)

So, Yajur Veda indicates that:~

They sink deeper in darkness those who worship sambhuti. (Sambhuti means created things, for example, table, chair, idol etc (Yajurved 40:9)

Those who worship visible things born of the prakrti, such as the earth, trees, bodies (human and the like) in place of God are enveloped in still greater darkness, in other words, they are extremely foolish, fall into an awful hell of pain and sorrow, and suffer terribly for a long time." (Yajur Veda 40:9)

Brihad Aranyaka Upanishad/ 3/8/9:~ It is in the truth that Imperishable, O Gargi, Brahman is not seen but is the seer, Brahman is not heard but is the hearer, Brahman is not thought but is the thinker, Brahman is not known but is the knower. There is no other seer but Brahman, no other hearer but Him, no other thinker but Brahman, no other knower but Brahman. And it is that Imperishable which is the warp and the woof of space.”

Thus, the Vedic scriptures recognize the unity of Reality or Brahman without any human intervention or intercession.

Religion and mysticism is a species of mesmerism affecting weaker or impressionable minds. Thus the panoply of a guru’s religious robes or presence of Godmen creates an unconscious suggestion in weaker minds of superior power or magical knowledge. Similarly, mass visitors to ashrams are suggested into thinking they experience great peace and their wishes will be fulfilled if they unconditionally surrender to Guru or Godmen.  Since they are unconsciously hypnotized into believing that will happen. However, when a strong mind which is aware of the truth meets a guru or Godmen are entirely unaffected.  Whatever happening within the waking experience is part of the duality, thus it cannot be part of the reality.

The metaphysics based on Vedas and Upanishads are beyond any form of theism be it monotheism or polytheism, as they point to “reality” which cannot be described by terms like monotheism or polytheism.

 The Vedas recognizes the “reality” both in its formless and manifest aspects. But today, the Vedic science and philosophy are demeaned, distorted and reduced by measuring it through an Abrahamic framework. Therefore, one has to bifurcate all the adulteration to grasp the real essence of Vedas and Upanishads to realize the ultimate truth which beyond form, time and space.   

Polytheism: While the so-called Hindus are based on Puranas, look at the disintegrated aspects of Reality or Brahman, the truth is that there is an inherent realization that all these aspects roll into the Reality or Brahman. The most often used example to dig out polytheism in Hinduism is the story of 33 million Gods in Hinduism. From the scriptures, we find a plethora of quotes that completely debase this myth.

Rig Veda 1/164/46:~ They call him Indra, Mitra, Varuna, Agni or the heavenly sunbird Garutmat. The seers call in many ways that which is One; they speak of Agni, Yama, Matarishvan.

Rig Veda 8/58/2:~ Only One is the Fire, enkindled in numerous ways; only One is the Sun, pervading this whole universe; only One is the Dawn, illuminating all things. In very truth, the One has become the whole world.

The religion of the Veda knows no idols

Max Müller says:- "The religion of the Veda knows no idols; the worship of idols in India is a secondary formation, a degradation of the more primitive worship of ideal Gods."

Therefore, there was no individual God or temples and worship in the Vedic religion, which existed prior to Buddhism.  Thus the individualized Gods and temples must have been built later on when the worships of the idol were introduced.  Thus the Vedic religion which existed in the past was free from idol and nature worship and idol worshiping rituals. 

Thus, the present day’s worship of individual Gods, created things, nature, and human are against Vedic teachings, and it looks like it has been fabricated and introduced by priestcraft. Since it, has passed on from one generation to the next it is hard for the people to believe the truth of their own religion, because they have sentimentally and emotionally involved in it and they refuse to accept anything else other than their inherited beliefs.  

Even Upanishads confirm that it is impossible to find and realize the truth via religion and scriptural study.:~Santthosh Kumaar