Kena Upanishad 2:4 When it is known through every state of cognition, it is rightly known, for (by such knowledge) one attains life eternal. +*****

The diamond does not know it is the diamond nor the light knows itself as light. The one who recognizes it as a diamond, and its light as light,  is neither a diamond nor its light but it is the man. 

Upanishads clearly says:~ 

Katha Upanishad 1:2:23:~ The Soul cannot be realized through hearing a scholarly explanation of the discourses, not even by the intellect.

Katha Upanishad 1:3:6:~ “Through the knowledge of the Soul, God, one is pure and clean constantly.” Neither by reading the books nor by taking a bath at holy place has one become pure. Inner purity is possible when one remains in constant touch with the Soul. Constant Soul-Consciousness is real purity. 

Kena Upanishad 2:4:~ When it is known through every state of cognition, it is rightly known, for (by such knowledge) one attains life eternal. Through one's own Self one gains power and through wisdom, one gains immortality. 

Kena Upanishad 2:5:~ If here one knows it, then there is the truth, and if here one knows it not, there is a great loss. Hence, seeing the Real in all beings, wise men become immortal on departing from this world. 

Mundaka Upanishad 1:2:8:~ “Remaining in the fold of ignorance and thinking “we are extremely wise and learned,” the fools with boastful nature ramble about like the blind led by the blind alone.” 

Mundaka Upanishad 3:2:3:~  “The weak and timid cannot realize the Self. Self-Realization is not possible through intellect or hearing the spiritual discourse. One who welcomes God in every activity, through a thorough controlled and disciplined life, to him also the Soul is revealed." 

Mundaka Upanishad 3:2:3:~ The Soul cannot be realized by the weak and timid.

That is why Sage Sri, Sankara says:~ VC:- 56- Neither by Yoga nor by Sankhya, nor by work, nor by learning, but by the realization of one's identity with Brahman is Liberation possible, and by no other means. 

58. Loud speech consisting of a shower of words, the skill in expounding the Scriptures, and likewise erudition - these merely bring on a little personal enjoyment to the scholar but are no good for Liberation.

59. The study of the Scriptures is useless so long as the highest Truth is unknown, and it is equally useless when the highest Truth has already been known.

60. The Scriptures consisting of many words are a dense forest which merely causes the mind to ramble. Hence men of wisdom should earnestly set about knowing the true nature of the Self.

61. For one who has been bitten by the serpent of Ignorance, the only remedy is the knowledge of Brahman. Of what avail are the Vedas and (other) Scriptures, Mantras (sacred formulae) and medicines to such a one?

62. A disease does not leave off if one simply utter the name of the medicine, without taking it; (similarly) without direct realization one cannot be liberated by the mere utterance of the word Brahman.

63. Without causing the objective universe to vanish and without knowing the truth of the Self, how is one to achieve Liberation by the mere utterance of the word Brahman? — It would result merely in an effort of speech.

64. Without killing one’s enemies, and possessing oneself of the splendor of the entire surrounding region, one cannot claim to be an emperor by merely saying, ‘I am an emperor’.

Till one realizes the truth beyond the form, time and space, whatever he knows about God is merely a belief. Belief is not the truth. Belief is individual whereas the ultimate truth is universal every belief system has its own idea of God thus there is no universality in the belief system. : ~ Santthosh Kumaar