Atman is actually nothing but Brahman (God in truth).+

Sage Goudpada says that: ~  'The merciful Veda teaches Karma and Upasana to people of lower and middling intellect while Jnana is taught to those of higher intellect.

So,  he clearly indicates rituals and theories are not meant for those who are searching for higher knowledge or wisdom.  

Ish Upanishads: ~ Vidya and Avidya both are hindrances to Self-knowledge, but Vidya is even worse than Avidya. The word Vidya is used here in a special sense; here it means worshipping Gods and Goddesses. By worshipping Gods and Goddesses, you will go after death to the world of Gods and Goddesses. But will that help you? The time you spent there is wasted because if you were not there you could have spent that time moving forward towards Self-knowledge, which is your goal. In the world of Gods and Goddesses, you cannot do that, and thus you go deeper and deeper into the darkness.

Avidya is Karma and, therefore, a hindrance. You perform Avidya ~ i.e., you perform Agnihotra and other sacrifices. This is a roundabout way of purifying the mind, and it is also groping in the dark. But it may not have as heavy a toll on your time and energy as the other.

Remember:~

Sage Sankara says: ~ Atman is Brahman. The Atman alone is real and is not religious truth.  Sage Sankara declared this Advaitic truth, which is the ultimate truth to the whole world, many centuries back is the rational truth, scientific truth, and ultimate truth.

Thus, the Atman which is present in the form of the consciousness is real and eternal, the world in which we exist is merely an illusion.  

Sage Sankara’s Supreme Brahman is impersonal, Nirguna (without Gunas or attributes), Nirakara (formless), Nirvisesha (without special characteristics), immutable, eternal, and Akarta (non-agent). It is above all needs and desires. It is always the Witnessing Subject. It can never become an object as it is beyond the reach of the senses. Brahman is non-dual, one without a second. It has no other besides it. It is destitute of difference, either external or internal. Brahman cannot be described because the description implies a distinction. Brahman cannot be distinguished from any other than It. In Brahman, there is not a distinction between substance and attribute. Sat-Chit-Ananda constitutes the very essence or Svarupa of Brahman, and not just Its attributes. The Nirguna Brahman of Sage Sri, Sankara is impersonal

The Soul, the ‘Self is the Infinite God. 

The Soul is the innermost Self. God is the Soul, which is present in the form of consciousness. God is the fullness of the consciousness without the illusory division of form, time, and space.  Therefore, there is nothing apart from it. 

God is Self-evident. God is not established by extraneous proofs. It is not possible to deny God because God is the very essence of the one who denies it. God is the basis of all kinds of knowledge, presuppositions, and proofs. God is within the universe in which you exist, the God is without the universe in which you exist.

The Vedas confirm God is Atman (Spirit), the Self.

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) is in the form of the Athma, and it is indeed Athma itself.

People, who worship the belief of God, are hallucinating that they become one with such God.

Vedas itself declares: May ye never accept another God in place of the Atman nor worship other than the Atman? Thus, to know the real God Self-realization is necessary. Self-realization is God-realization. Self-realization itself is real worship.

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)

How can you worship God? That implies two ~ the worshiper and the worshiped, whereas God is nondual. One can worship his idea of God only or realize his unity with it when he can’t worship it as apart.

When Upanishads and Vedas declare that, “God is in the form of the Athma, and God is indeed Athma itself” then why accept another God in place of the Atman nor worship other than the Atman.

God is the Supreme Being the One eternal homogeneous essence, indivisible consciousness, and intelligence, which is beyond form, time, and space. Which the Sages describe in a variety of ways through diverse words.

Bhagavad Gita: ~ ‘All those whose intelligence has been stolen by material desires, they worship many Gods. (7- Verse -20)

Only the path of wisdom leads the seeker of truth on his journey to the ultimate realization of the true nature of the Universal Essence, which is the Soul. The Soul is present in the form of consciousness.

Bhagavad Gita: 7: 19:~ "Such a man who has attained true knowledge, the knowledge of Self, the knowledge of Atman, worships ‘Self’ as~ Atman (God) alone exists~ everything is Atman, there exists nothing except Atman. Such a man is extremely rare."

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 duality, no differentiation. Only Atman exists.

Ishopanishad:~  "They are steeped in ignorance and sunk into the greatest depth of misery who worships the matter, instead of the All-Pervading God and those who worship things born of matter like trees, animals, man, etc. are sunk deeper in misery."

Katha Upanishad says: ~Fools dwelling in darkness but thinking themselves wise and erudite, go round and round, by various tortuous paths, like the blind led by the blind. (Ch II-5 P-14 Upanishads Nikhilananda)

It indicates that the one who is ignorant (darkness) of the Soul, the innermost  Self (Atman) searches for truth by accumulating knowledge of every path and practice and uncertain about the truth, and thinks every path leads towards reality. Ignorance of the true Self leads one towards unreality or hallucination.

Bhad Upanishad: ~ This Self is dearer than a son, dearer than wealth, dearer than everything else because It is innermost. If one holding the 'Self' dear were to say to a person who speaks of anything other than the Self as dear, that he, the latter, will lose what he holds dear—and the former is certainly competent to do so—it will indeed come true. One should meditate upon the Self alone as dear. He who meditates upon the Self alone as dear—what he holds dear will not perish. (8-p- -211)

It is the first instance of monism in organized religion. Vedic religion remains the only religion with this concept. To call this concept 'God' would be imprecise.  The closest interpretation of the term can be found in ~ 

Tattireya Upanishad (II.1):~ where Brahman is described in the following manner: Satyam Jnanam Anantam Brahman - "Brahman is of the nature of truth, knowledge, and infinity". Thus, Brahman is the origin and the end of all things, material or otherwise. Brahman is the root source and Divine Ground of everything that exists and does not exist. It is defined as unknowable and Satchidananda (Truth-Consciousness-Bliss).

Since it is eternal and infinite, it comprises the only truth. The goal of Vedic religion, through the various yogas, is to realize that consciousness (Atman) is actually nothing but Brahman. :~Santthosh Kumaar