Every vibration has a corresponding sound and everything in the universe has a vibration and thus a sound. Each atom, molecule, cell, object, group of objects, even the entire universe, has its own collection of vibrations and unique sound.
When you chant a mantra, you merge with the sound vibration and become at one with the energy wavelength of the object of your mantra. Mantra chanting makes you at one with everyone, everywhere who is chanting that mantra and with everyone who has ever chanted the mantra. All the saints who have ever reached enlightenment through the technique of chanting that mantra connect with you as you connect with the vibration of the mantra. You merge with their essence which has been purified and is holy and you become pure and holy because that divine level of existence vibrates only with holiness, peace, and bliss.
By chanting a mantra, your cells, molecules, atoms, and sub-atomic particles all vibrate in the same wavelength as the mantra. Once attuned with this vibration you connect with everything resonating on that plane of existence. It’s like tuning a radio. At first you may get static, but once you are in the right frequency your reception is perfect. Om is the universal sound. It is within every word and within everything. So when you chant Om, you merge with all energy and all forms, from the sub-atomic to the universal, from the most gross to the most divine. And when you are tuned in perfectly, you will receive holy frequencies clearly and merge and emerge at one with the source of all and live happily ever after.
Many meditation teachers suggest that it is necessary to understand every intellectual aspect of the meaning of the mantra that is being practiced, but just as many others feel that the intellect may tend to confuse and hold back spiritual progress. What both types of teachers agree on is that mantras have the potential to take practitioners to the level of consciousness that transcends the limitations of the mind by a billion-fold. There is an ancient tale that very well shows that true devotion and complete absorption are the key:
Once upon a time in a land far away lived a poor uneducated, mentally challenged man who tended a herd of cows for his master. He happened upon a meditation teacher and was very taken with his calm, loving, gentle and happy nature. He decided he wanted to know that experience first hand. And so he went to the teacher and begged him to teach him a way to achieve the inner peace that radiated so obviously from the teacher. The teacher accepted him as his student but quickly found that the man couldn’t understand any of the philosophical points he was making and as a matter of fact couldn’t even remember the mantra Om when he tried to teach it to him. The teacher lovingly said, "My oh my, you don’t seem to know anything at all, can’t be taught, and can’t remember anything. You are devoted and sincere in your desire to gain happiness though, so I will try to help you. My son, what do you know?" The man said, "Oh great teacher, the only thing I know is cows. All my life I’ve spent caring for cows, making sure they graze, are milked, and are kept clean. Yes, for me, everything is cows." "Well, that’s alright," said the teacher, "then you know what sound the cows make." "Oh yes," said the man, "they say moo." "Very well then," said the teacher, "for you, moo will be your mantra. All you have to do is say moo continually and you will reach freedom from suffering and know real bliss." So the man chanted moo, moo, moo when he took the cows out to graze and he chanted moo, moo, moo when he milked them, and he chanted moo, moo, moo when he cleaned them. He chanted moo all the time and very soon merged with that vibration, which is Om backward, and reached the highest heights of joyous understanding and lived happily ever after.
From this story, we learn that it is virtually impossible to chant Om "wrong". It is, after all, an insentient sound. But the giver of this sound to the universe knows the intention and devotion of the practitioner and that is by what we will be rewarded. It is said that one minute of sincere chanting is superior to a thousand hours of mere sounding of the words. A parrot can be taught to recite a mantra but this will be just mere vibrations in the air. It is the love and worship behind the sound that counts. Technically though, there is a "correct" way to chant Om. It is made up of three letters: A, U, M. These contain all the sounds there are. The A is guttural and comes from the throat. It is pronounced without any part of the tongue or palate in contact. The U sound comes from the middle of the sounding board, the palate. In Sanskrit, the A and U join together to become O. The O sound is vibrated from the navel/ solar plexus area and sent up to the sternum to the voice region, the lips, where the M sound is prolonged and vibrated up to the crown of the head. This vibrating M is felt in every cell of the body and is beamed out lovingly, soothingly, powerfully, to everything, everyone, everywhere. Intellectually and metaphysically, A stands for the physical world perceptible to the senses, the material world. U represents the astral and dream planes, heaven and hell. M is the unknown, deep sleep, and that which is unfathomable to the intellect. Thus Om contains the entire spectrum of sound, words, worlds, and concepts. Om represents the source of all light, love, and wisdom.
There are three ways to do mantras - aloud, silently but while mouthing or humming the mantra, and completely silently within oneself. When done aloud and particularly when done with others, the sound of Om is energizing, calming, and healing. Although it is often encouraged to do your mantra all the time, it would certainly be questionable to consider chanting Om aloud in the middle of a board meeting. Similarly, it may be preferable to do Om silently just by moving your lips if you are in a movie theater. Chanting Om completely silently is considered the most potent method because it is not dependent on having a human voice box, or lips, or facial muscles, all of which are temporary manifestations compared to the billions of years you will be fully at one with Om. It is advantageous to spiritual development to consider the theological, philosophical and mystical aspects of Om while chanting with your physical eyes closed, looking through the third eye, and paying attention to your breath. This may seem complex and complicated, but once in synch, it happens naturally as Om reveals itself, your Real Self, to you.