Tulsidas, the author of Ramcharitmanas says, 

"Gira artha jal bichi some kahiyat bhinna Na bhinna." i.e. the word and its meaning are mixed and are inseparable like water and wave (Baal Kanda).  

Power of word has always been recognized for its positive and negative effects. They can be potentially constructive as also substantially destructive. During Vedic age, words used were merged with potential divinity and had a powerful effect and liberating purpose. It always conveyed something enlightening. in form of mantras.  

Word is the outer part and meaning or thought is its inner part. Every word has a meaning or a thought and so every thought finds expression only through word. This is language. Language was never invented by some people at any point of time in any assembly of linguistic nature which decided on words; which particular word to represent which idea or which particular thought. It really took its own time to evolve gradually and quite unconsciously. It has always been difficult to identify a word fixed with a particular thought or meaning. Many words can be used for a particular thought expression. Even with difficult words at different times, over the ages, that very idea, thought or meaning might have been differently identified. This much is true that words contain an idea or thought. No word is possible to exist without such expression and every thought has a word to express it.  

Now there is the question of sound (Phonetics).  It is not necessary that the word be bound with the same sound ever. Every sound is affected by time and varies among people. Thus we see that the pronunciation and accent may differ and vary but the relationship of a thought with a word remains unaffected and unchanged. Sound is called Sabda in Hindi. Sound is not merely a noise but it has levels of meaning. It isSphota that comes out from the eternal power of Shakti. It may mean Nada to a poet and the seer, or Anahata (Potential Thought) that is unexpressed. Every Sabda has its own inherent power as we see in the bells drums and in the mantras. Does not the drum of Siva Manifest?  

Creation? Sabda Brahman thus comes to be understood as the ultimate sound without any attribute, indicative of realization of Brahman. 

It is clear that the word is a symbol for a thing signified. The thing so exists but its symbol may vary through ages and from time to time, without disturbing the relationship with the thing so signified. One may not see that thing but may know it by symbol. The meaning of the word will bring forth what the symbol means or what the thing symbolizes .The frequency and sound is so sequenced as to appeal to the inherent Shakti or potency. The word mantra as divine word was potent enough to heal the ailments, lessen sufferings and grant peace of mind. It was many millennium later the gospel of John said that, “In the beginning was the word and the word was with God. All things were made through Him and without Him was not any thing made that was made” (John 11-4). 

The Jews and Islam religions have the names of God with the base of EL or AL , which means one or the All Hebrew book of Genesis gives a word “Elohin “ which signifies, ”The one that is many “.  Jesus spoke of God as Aloha in Aramaic, meaning, “One moving through all souls“.  In Islam, Allah has both the roots AL and La.  Quran says, ”Allah is there, one light that illuminates heaven and earth".  For Hindus the word that all the Vedas glorify, all sacred studies and holy life seek – that word is AUM (also written as OM).  Chandogya Upanishad (1-2 ) says, ”As earth comes from the water, plants from earth, a man from planets, so man is speech and speech is AUM.. Of all speech, the essence is Rg Veda but same is the essence of Rg Veda and same is the essence of AUM, the Udageeth.” 

Swami Chinayananad in Kathopanishad, page 104, writes, ”It is interesting to know that the word AUM is not found in Rg Veda or Atharva Veda but occurs in the Taittareya Samhita of the Yajur Veda. This word is a symbol of primal vibration through which the universe manifests. It is the very first thought of God. It is the power differentiating the oneness into multiplicity. This is the most sacred symbol in Hinduism. It greatly appeared in the Upanishads it is regarded as seed of all mantras, containing all origination and dissolution; it is Pranava (reverberation) and the supreme Aksara (Syllable)".

There is only one God and He alone is the creator of the Universe. So the idea of God remains common in all the religions but they use different words to express Him.  There is nothing like a Christian God or an Islamic God or a Hindu God. He is the God of all mankind and of all the creation.  All religions have attempted to express the nature of the Supreme Being in a single word and AUM is the very natural symbol of Hindus. Yajur Veda (XI-! 7) says, ”AUM is the great God who is omnipresent like ether.”  Chandogya Upanishad says, ”He alone, whose name is Aum, who is immortal, is worthy of our adoration and none other.”  Manduk 1-1 says, ”All the Vedas and the shastras declare AUM as the primary and natural name of God. All others are His secondary names.”  Kaivalya further goes to say, ”He is called Brahman, the maker of the universe; Vishnu, All pervading; Rudra, the punisher of the wicked; Shiva, blissful and benefactor of all;  Akshara, immortal and omnipresent;Swarat, self-effulgent; Kalagni, cause of the dissolution of the world and regulator of Time; Chandrama, the true source of happiness.“  None of the God’s name is meaningless. They are all connotative.  It should be clearly understood that AUM is the name of God only and of no other object, material or spiritual. Other names are based on the subject under treatment and the adjective that qualifies. Such as Agni, Virat Kalagni or Rudra, the words that that signify the natural objects of the world also. 

We produce a sound by using the larynx or the palate as the sound board. The sound has to be most natural, easy flowing and all inclusive. AUM is such a sound. The first letter is A. It is the root sound. While pronouncing it, no part of tongue or palate is touched. It comes quite naturally. Then at the end of the last sound of series comes the letter M.  While pronouncing M, the lips get closed, as the sound comes to close which indicates that there can be no further sound. It is the last one. In between the sound, is the letter U, like a roller, between A and M, rolling from the very first root A to the last one M, which is the end of the sound with mouth closed. Thus from the first go to the last close, there is a natural continuity of sound which represents the whole sound production system. Thus we see that AUM comes as very natural symbol embodying all and every thing.  

AUM is an accepted symbol, adopted in practice by religious thoughts in India. The word AUM (AUM) is complete in it and signifies all functions. The Buddhists, the Sikhs and the Jains adopted it in their own ways.  

Rg Veda prays, ”Mayest Thou AUM, O God, who art Mitra, friend of all; Varun, holiest of all, and Aryama, controller of the entire universe, be merciful to us. Mayest Thou Indra, O Lord Almighty, Brihaspati, the Lord of the universe, the support of all, endow us with knowledge and power, Mayest Thou Vishnu, O Omnipresent, and Urkrama, omnipotent being; shower thy blessing all around us. AUM.”  AUM is uttered in the beginning and conclusion of a prayer. The sacred symbol AUM is a particle implying consent is a manifestation in sound of the Ultimate Reality.  It is clear that AUM is made up of three, connected but distinct elements pointing to Brahman, Vishnu and Mahesh in its own ways. AUM imbibes, embodies and signifies each and every aspect and is possessed of a natural sound system and symbolic significance. 

Vivekananda says,” Ishvara (God) is the Atman as seen or grasped by the mind. His highest name is AUM --- Repeating AUM continually is the only true worship. It is not a word – It is god Himself. “(Vedanta Voice of Freedom p. 266).