Every letter is a Bija akshara (seed-letter of a sacred word); so I do not whisper secretly any Mantra in your ear. I am giving it in every word .I speak. Listen to Me. When you wake up, feel that you are entering the stage to play the role assigned to you by the Lord; pray that you may act it well and earn His approbation. At night, when you retire to sleep, feel that you are entering the green-room after the scene, but with the dress of your role on; for perhaps the role is not yet over and you have not yet been permitted to take the dress off. Perhaps, you have to make another entrance the next morning. Do not worry about that. Place yourself fully at His disposal; He knows. He has written the Play and He knows how it will end and how it will go on. Yours is but to act and retire. (SSS Vol.2, p. 104)
The five-element body of man equipped with five senses has as its life-breath the five-lettered formula, enshrined in the Namaka section of the Yajur Veda – ‘Namah Si-vaa-ya’. It is a basic Mantra, which means, ‘that which can save, when meditated upon.’ Every Mantra has a seed-sound (Bija akshara) which precedes it and provides it with additional potency. Sound emanated first through the will of God. So the Bija akshara is fundamental for the Mantra and its efficacy. The Akshara is sanctified by the Vedas or by the Tantra texts. The Bija akshara for the five-lettered Namah Shivaya is the Vedic sound, Om.
Om is how A, U and M are jointly pronounced. Each of these letters is devoid of spiritual force but, together, they arouse energising vibrations. ‘Shivaya’ in the Mantra means ‘to Shiva’. ‘Shiva’ is That which confers good fortune, wealth, prosperity and happiness. Pundits have commented on this formula and explained it in various ways. They have interpreted ‘Na’ as indicating Nandivahana, the God who has Nandi (the Bull) as Vahana (vehicle). They take ‘Ma’ as the pointer to another Name of Shiva, Mandaramalin (wearing a garland of Mandara flowers) and ‘Si’ as Surya (the Sun which when it dawns on earth unfolds the Lotus of the Hearts of Beings etc). Each one allows his imagination to lead him along.
But, the formula contains a more universal and abstract concept. It has to be pronounced always with Om. The Namah (prostration) is for Om which is denoted as having the Shiva attribute (being the source of peace, prosperity and success, of Mangalam in short). The process of worship is best described by Pothana in the Bhagavatam he has rendered in Telugu.
Pothana speaks of ‘chethulara Sivuni Puja’ (worshipping Shiva with the hands). By ‘hand’, he means, the ‘five-fingered’, representing the five-lettered Mantra. Shiva is the five-element-lord and so He has all the power and wealth the five can yield to man who is himself a composite of the five! (SSS Vol.18, pp. 125-126)