Swami Vivekananda on the symbolism of Om in Hinduism - Source complete works of Swami Vivekananda.
Hindu mystics say the manifesting word of God is Om. Why emphasize the word Om? There are hundreds of words for god. One thought is connected with a thousand words, and each one stands as a symbol for god. But there must be generalization among all these words, some substratum, some common ground of all these symbols, and that which is the common symbol will be the best and really represents them all. In making a sound, we use the larynx and the palate as sounding boards. In pronouncing the word Om, the first letter, A, when pronounced, no part of the tongue is used, and when pronouncing M or UM, the lips are close. In other words, in pronouncing the word Om, or Aum, no part of tongue and palate is used.
Every idea in mind has a counterpart in a word; the word and the thought are inseparable. So long as man has existed, there have been words and languages. What is the connection between an idea and word? The thought may be the same in several languages of the world, yet the language is different. We must have a word to express each thought, but these words need not necessarily have the same sound. The sounds vary, yet the relation between the sounds and the thoughts is a natural one. The connection between thoughts and sounds is good only if there is really a real connection between the thing signified and the symbol; until then, that symbol will never come into general use.
A symbol is the manifester of the thing signified, and if the thing signified has already an existence, and if, by experience, we know that the symbol has expressed that thing many times, then we are sure that there is a real relation between them.
There must be a natural connection between the symbol and thing signified; then, when that symbol is pronounced, it recalls the thing signified.
Hindu mystics say the manifesting word of God is Om. Why emphasize the word Om? There are hundreds of words for god. One thought is connected with a thousand words, and each one stands as a symbol for god. But there must be generalization among all these words, some substratum, some common ground of all these symbols, and that which is the common symbol will be the best and really represents them all. In making a sound, we use the larynx and the palate as sounding boards. In pronouncing the word Om, the first letter, A, when pronounced, no part of the tongue is used, and when pronouncing M or UM, the lips are close. In other words, in pronouncing the word Om, or Aum, no part of tongue and palate is used.
Thus, Om represents the whole phenomena of sound-producing. As such, it must be that natural symbol, the matrix of all the various sounds. It denotes the whole range and possibilities of all the words that can be made. All this can be speculative, yet all the religious ideas of the Vedas have gathered themselves around this word – Om.
The use of the word God covers a limited function since people have to add an adjective to make it personal, impersonal, or absolute. But the world Om signifies everything spiritual.