If you think there is another entity whether man or God there is no truth

Truth is not only that which is beyond contradiction, but also that in which is no possibility of contradiction. Such a state can only be realized as non-duality, where there is no second thing other than consciousness. The illustration for that is deep sleep but sleep is not the ultimate reality. It is merely an analogy.

 Brihad Upanishad declares:-, "If you think there is another entity whether man or God there is no truth." This is the teaching since time immemorial of those who have inquired into truth.

Consciousness alone which is permanent and eternal, unchanging in the changing world is reality. People hear of Brahman or ultimate truth. People can only imagine it. One requires words only to distinguish between is there and not there, but he can’t posit either of Reality, because his saying so is only an idea, not reality. Ultimate truth is beyond words. Words are of use, however, as a thorn to pull out the thorn of other words that hinder knowledge.

Intellectually knowing the truth is only an imagination, whereas realizing the truth is knowing it as such.

Thus orthodoxy which misleads the seekers of truth, therefore seeker of truth has to verify the truth on his own by reason based on the consciousness as self then only accept the un-contradictable truth.  

And also in Yajurved says:

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 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.]

When Yajur Veda declares that they are extremely foolish, fall into an awful hell of pain and sorrow, and suffer terribly for a long time."

 When the religion of the Veda knows no idols then why so many gods and goddesses with different form and name are being propagated as Vedic gods. Why these conceptual gods are introduced when Vedic concept of god is free from form and attributes. 

Who introduced concept of god with attributes and attributeless gods, when Yajur Veda says: -   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. Therefore, all these add-ons proves that the form and attribute based concepts are introduced by some sages of the past with new belief system and code of conducts in the name of Vedas. 

 Sruti is made the final or exclusive authority in apara Vidya and that for supporting the tenet of the CAUSAL relation or creatorship of Brahman, Nirguna Brahman = the "Absolute beyond qualities," which can be defined only in a negative way. For the Shankarian school = the Ultimate Reality, higher than the Lord. i.e. of Saguna or apara Brahman ... The support of Scriptural Revelation is, therefore, absolutely necessary for this hypothesis of cosmology, this Saguna or apara (= inferior) Brahman, but not for the absolute truth of Nirguna Brahman.

  The Sruti itself says: "This Atma is NOT to be attained by a study of the Vedas.  [Katha Upanishad I, 2, 23.] 

          

Therefore, all the non- Vedic add-ons and attribute based knowledge, which are inferior, have to be bifurcated and excluded to know the ultimate truth.  The seeker of truth has to drop all the inferior knowledge based on the attributes and go beyond Vedas to understand assimilate and realize the ultimate truth or Brahman.