Yajurveda says:~ If you worship what is not God in place of the real God fall into an awful hell of pain and sorrow, and suffer terribly for a long time.+

Yajurveda says:~  If you worship what is not God in place of  the real 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."

Translation 1

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

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

Those who worship visible things born of the Prakriti, 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.)

The Hindus believed in polytheism, believing all of their Gods to be separate individuals, which was introduced much later by the founders of Hinduism which contains diverse beliefs caste, and creed to help the ignorant populace.  

Many Gods and Goddesses with different forms and names are being propagated as Vedic Gods by the saints and founders of different caste and creeds in the past. All these conceptual Gods have introduced in place the Vedic concept of God which is free from form and attributes.  Puranic Gods are non-Vedic Gods. Worship of Such Gods is barred in Vedas.  

Brihadaranyaka Upanishad:~ "He who worships the deities as entities entirely separate from him does not know the truth. For the Gods, he is like a pasu (beast)". (1. 4. 10)

Sage Sankara says Atman is Brahman (God in truth). 

That is why Sage Sankara,  VC-  v6~ Let erudite scholars quote all the scripture, let Gods be invoked through sacrifices, let elaborate rituals be performed, let personal Gods be propitiated---yet, without the realization of one‘s identity with the Self, there shall be no liberation for the individual, not even in the lifetimes of a hundred Brahmas put together.

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  Sankara is impersonal

The God you see and meet and in your vision is not God in truth but a hallucination.  How can you see and meet God without knowing what God is in actuality? Praying and meditating on God without knowing what God really is, leads to hallucination.    The world in which you exist hides God. Thus, Self-realization is necessary to realize ‘what God is in actuality.  

The Atman, the ‘Self is the Infinite God. 

The Atman is the Self. God is the Atman, 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 present 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  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 worshipper 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 or 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."

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 duality, no differentiation. Only Atman exists.

Brihadaranyaka Upanishad IV-13:~ ‘As a mass of salt has neither inside nor outside, but is entirely a mass of taste, thus indeed, has that Self neither inside nor outside but is altogether a mass of Knowledge. Just as a lump of salt has inside as well as outside one and the same saltish taste, not any other taste, so also that Brahman (consciousness) has inside as well as outside one and the same intelligence. Inside and outside are mental creations only. When the mind melts in silence, ideas of inside and outside vanish. The sages cognize one illimitable, homogeneous mass of consciousness only.

Causality taught in the Upanishads is only to enable us to understand the supreme truth of no-origination. The world is not different from the consciousness and consciousness is not different from the Soul, the Self, and the Soul is not different from the ultimate truth or Brahman. That consciousness appears as a diverse world is only an illusion. If it really became diverse then the immortal would become mortal.

The dualists who seek to prove the origination of the unborn, by that very enterprise try to make the immortal, mortal. Ultimate nature can never change - the immortal can never become mortal and vice versa.

Sage Goudapada quotes from the Upanishads: ~ "There's no plurality here"; "The Soul through its powers appears to be many"; "those who are attached to the creation or production or origination go to utter darkness"; "the unborn is never reborn, for what can produce it?”

Thus, the goal is to realize Self-realization.  Atman (consciousness) is nothing but Brahman (God). Realizing Atman (consciousness) as Brahman (ultimate truth) is truth realization or Self-Realization, the Self-realization is God-realization. :~Santthosh Kumaar