When Sage Sankara himself declares : Atman is Brahman (God) then why to accept anything else as God other than Atman.+

Remember this; Hinduism is not Ancient Vedic religion or Santana Dharma, which existed prior to Buddhism and Jainism.

Hinduism is not the Ancient Vedic religion or Santana Dharma. And all Hindus indulge in non-Vedic practices barred by the Vedas introduced by the different founders of the different sects of Hinduism at different times, whereas the Vedic religion or Santana Dharma is ancient and has no founder. 

All the non-Vedic caste-based belief systems founded by different founders of Hinduism have to be dropped to realize Ancient Vedic religion or Santana Dharma is nothing to do with present-day Hinduism.

Hindus indulge non-Vedic beliefs such as idolatry, ancestor worship, pilgrimages, priestcraft, offerings made in temples, the caste system, untouchability, child marriages, and sati. All these lack Vedic sanction.

The Vedic system did not have a caste system. The caste system was a fake created in the name of Hinduism. This non~Vedic belief system called Hinduism creates hatred in the low caste Hindus for the higher caste is not the Vedic idea.

Brahmin was never a caste in the ancient Vedic society, and Chaturvarna was a professional classification and not a caste system as is being projected today.

Terming the original Chaturvarna system as the caste system is like saying that the classification of people as doctors, engineers, and laborers today, is the caste system.

To be considered an orthodox Hindu one need only accept the authority of Shruti, however, there is no universal agreement amongst Hindus on what constitutes Shruti. Vedantins consider the Vedanta, i.e., the Upanishads as Shruti but also include the Bhagavad-Gita and Brahma Sutras as authoritative. For some Vaishnavas, the Bhagavata Purana is to be considered Veda. Some consider the Tantras are considered Veda. Thus, we find that there is ample scope for different philosophies and practices under the very broad umbrella of Hinduism.

The people of India adopted Buddhism, Jainism, and many other splinter groups with non-Vedic ideologies with new beliefs, new Gods rituals, dogmas, and superstitions.

All the mythological heroes of the mythological stories are projected as real gods. All the mythological stories are nothing to do with Vedas. There is no mention of these mythological Gods in the Vedas. Thus, the ancient Vedic religion or Santana Dharma disappeared without a trace.

Reincarnation was not a Vedic belief. Belief in reincarnation which is central to Hinduism of today is not attested to in the Vedas though they hint at life after death. The doctrine of transmigration as elaborated in Hinduism has no place in the Vedic hymns”. In the early Vedic literature, there is no express mention of the doctrine of transmigration.

It is in the Upanishads that it appears for the first time. The Rig Veda speaks of two paths for the Souls of the deceased, namely, the path of the Gods (devayana) and the path of the fathers (pitriyana). Those who go by the former enjoy immortality and there is no return to physical life after that.

The Vedic man longed for this state of life. Whereas those who go by the latter path, unite with the Father and then return to earth, after having enjoyed the fruits of his deeds.

Rig Veda ~ consists of about 10,500 verses ― there is only one occasion where there is mention of a return to this world after death. What is implied here is that it cannot be taken as important teaching of the Rig Veda.

The Avatara and caste system are not Vedic in origin. The theory of Avatara (‘descend’) of Gods which is very important to modern Hinduism is non-Vedic. The term Avatara (…) is not found in the earlier Vedic texts and is absent from the older Sanskrit glossaries

The religion of the Veda knows no idols, then why so many Gods and Goddesses with different forms and names are being propagated as Vedic Gods? 

Why these conceptual Gods are introduced when the Vedic concept of God is free from form and attributes?

The God of Santana Dharma or Vedic religion is Athma. Athma is the Soul, the innermost 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 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: ~ “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, and 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.

Yajurveda – chapter- 32:~  God is  Supreme Spirit has no ‘Pratima’ (idol) or material shape. God cannot be seen directly by anyone. God pervades all beings and all directions. 

Thus, Idolatry does not find any support from the Vedas.

Brihadaranyaka Upanishad: ~ Brahman (God in truth) is in the form of the Athma, and it is indeed Athma itself.

When Yajurveda says that God is  Supreme Spirit has no ‘Pratima’ (idol) or material shape then whatever the Indian innocent populace believes and worships today are non-~Vedic Gods. All the mantras and prayers are based on non~Vedic Gods.

From the Vedic perspective, all non-Vedic Gods are a myth. Worshipping myth in place of real God barred by Vedas.

The religion of the Veda knows no idols, then why so many Gods and Goddesses with different forms and names are being propagated as Vedic Gods? Why these conceptual Gods are introduced when the Vedic concept of God is free from form and attributes?

Yajurveda gives clear-cut instructions on what not to worship in place of God in truth: ~

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 than those who worship sambhuti. (Sambhuti means created things, for example, table, chair, idol, etc.) (Yajurveda 40:9)

Translation 2

"Deep into the shade of blinding gloom fall asambhuti's worshippers. They sink to darkness deeper yet who on sambhuti is 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.)

Yajur Veda clearly says:~

They sink deeper in darkness than 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, and 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.)

Sage Sankara says: ~ Atman is Brahman. Thus, the Soul the innermost ‘Self’ is God. Therefore, all the Gods with form and attributes are mere imaginations based on the false self. Thus, there are adulteration and add-ons in the past, which have to be bifurcated if one wants pure Vedic essence.

This indicates the nature of the ‘Self’, which is the Soul. Thus, the Soul is the ultimate truth of Brahman or God in truth. 

When the Soul is the ultimate truth or God why indulge in worshiping the belief individualized God, which is not God? The Hindu belief system which came into existence after the 2nd century is nothing to do with the Vedas and Vedic religions.

The ultimate truth or Brahman is God in truth. God in truth is not the religious God we believe in and worship.

Those who want to know the truth of the Vedic religion or Santana Dharma have to discard the non-Vedic belief system founded by different founders of Hinduism which propagates falsehood as truth.

When Sage Sankara himself says:~ Atman is Brahman (God in truth) then why accept anything else as God other than Atman?

Sage Sankara is a Vedic Sage of universal order projecting him as a non~Vedic Sage is a great sin. 

The Vedic truth is pure spiritual truth. The essence of the Vedas is pure spirituality. Advaita propagated by Sage Sankara is pure spirituality. Advaita is nothing to do with Advaitic orthodoxy, which is meant for the ignorant populace. : ~ Santthosh Kumaar