Mantras are usually an essential part of a Sadhana and used for purification and transformation. A mantra has the longer to be repeated, the longer it is. A guru can often transfer a small part of his VAK to the student and thus multiply the effectiveness.
From Japa Yoga: A Comprehensive Treatise on Mantra-Sastra
A Bija-Akshara is a seed-letter. It is a very powerful Mantra. Every Devata has his or her own Bija-Akshara. The greatest of all Bija-Aksharas is OM or Pranava, for it is the symbol of the Para-Brahman or the Paramatman Himself. OM contains within itself all the other Bija-Aksharas. OM is the general source or the common seed from which all the particular sounds or secondary seeds proceed. The letters of the alphabet are only emanations from OM which is the root of all sounds and letters. There is no Mantra superior to or greater than OM. OM, as it pronounced ordinarily, is an outward gross form of the real subtle inaudible state of sound which is called the Amatra or the immeasurable fourth transcendental state. As the various Devatas are the aspects or forms of the One Supreme Being, so the various Bija-Aksharas or Bija-Mantras are so many aspects or forms of the Supreme Bija or Mantra, viz., OM. Even the letters 'A', 'U' and 'M' do not really give the transcendental or original state of sound. Even this triliteral sound is only an expression or manifestation of the highest primal Dhvani or vibration. The transcendental sound of OM is heard only by Yogins and not by the ordinary ear. In the correct pronunciation of OM the sound proceeds from the navel, with a deep and harmonious vibration, and gradually manifests itself by stages at the upper part of the nostrils where the Anusvara or the Chandrabindu is sounded.
Generally a Bija-Mantra consists of a single letter. Sometimes it constitutes several syllables. For example, the Bija-Mantra 'Kam' has a single letter with the Anusvara or the Chandrabindu which forms termination of all Bija-Mantras. In the Chandrabindu, Nada and Bindu are blended together. Some Bija-Mantras are made up of compound letters, such as the Mantra 'Hreem'. The Bija-Mantras have a significant inner meaning and often do not convey any meaning on their face. Their meaning is subtle, mystic. The form of the Bija-Mantra is the form of the Devata signified by it.
The Bijas of the five Mahabhutas or great elements, i.e., of the Devatas or the presiding intelligences of the elements, viz., Ether, Air, Fire, Water and Earth, are respectively Ham, Yam, Ram, Vam and Lam. The meanings of a few Bija-Mantras are given here, to serve as examples.OM
OM consists of three letters: 'A', 'U' and 'M'. It signifies the three periods of time, the three states of consciousness, the entire existence. 'A' is the waking state or Virat and Visva. 'U' is the dreaming state of Hiranyagarbha and Taijasa. 'M' is the sleeping state or Isvara and Prajna. Study the Mandukyopanishad in detail in order to understand the meaning of OM.HAUM
In this Mantra, Ha is Siva. Au is Sadasiva. The Nada and Bindu mean that which dispels sorrow. With this Mantra Lord Siva should be worshipped.DUM
Here Da means Durga. U means to protect. Nada means the mother of the universe. Bindu signifies action (worship or prayer). This is the Mantra of Durga.KREEM
With this Mantra Kalika should be worshipped. Ka is Kali. Ra is Brahman. Ee is Mahamaya. Nada is the mother of the universe. Bindu is the dispeller of sorrow.HREEM
This is the Mantra of Mahamaya or Bhuvanesvari. Ha means Siva. Ra is Prakriti. Ee means Mahamaya. Nada is the mother of the universe. Bindu means the dispeller of sorrow.SHREEM
This is the Mantra of Mahalakshmi. Sa is Mahalakshmi. Ra means wealth. Ee means satisfaction or contentment. Nada is Apara or the manifested Brahman or Isvara. Bindu means the dispeller of sorrow.AIM
This is the Bija-Mantra of Sarasvati. Ai means Sarasvati. Bindu means the dispeller of sorrow.KLEEM
This is the Kamabija. Ka means the Lord of desire (Kamadeva). Ka may also mean Krishna. La means Indra. Ee means contentment or satisfaction. Nada and Bindu mean that which brings happiness and sorrow.HOOM
In this Mantra, Ha is Siva. U is Bhairava. Nada is the Supreme. Bindu means the dispeller of sorrow. This is the threefold Bija of Varma of armour (coat of mail).GAM
This is the Ganesha-Bija. Ga means Ganesha. Bindu means the dispeller of sorrow.GLAUM
This also is a Mantra of Ganesha. Ga means Ganesha. La means that which pervades. Au means lustre or brilliance. Bindu means the dispeller of sorrow.KSHRAUM
This is the Bija of Narasimha. Ksha is Narasimha. Ra is Brahma. Au means with teeth pointing upwards. Bindu means the dispeller of sorrow.
There are, like these, many other Bija-Mantras which signify various Devatas. 'Vyaam' is the Bija of Vyasa-Mantra, 'Brim' of Brihaspati-Mantra and 'Raam' of Rama-Mantra.SRI VIDYA
Sri-Vidya is the great Mantra of Tripurasundari or Bhuvanesvari or Mahamaya. It is also called the Panchadasi or the Panchadasakshari, for it is formed of fifteen letters. In its developed form it consists of sixteen letters and is called Shodasi or the Shodasakshari. The aspirant should directly get initiation of this Mantra from a Guru, and should not start reading it for himself or doing Japa of it, of his own accord. This is a very powerful Mantra and, when it is not properly repeated, it may harm the Upasaka. So it is imperative that it should be got directly from a Guru who has got Siddhi of this Mantra.
The general rule is that this Mantra (Sri-Vidya) should be repeated after one's passing through certain stages of self-purification through other Mantras. In the beginning a Purascharana of Ganesa-Mantra should be done. Then Purascharanas of Gayatri-Mantra, Maha-Mrityunjaya-Mantra and Durga-Mantra (Vaidika or Tantrika) have to be done. After this the Panchadasakshari and the Shodasakshari have to be taken up for Japa.
The Bija-Mantras and the Sri-Vidya should not be repeated by those who are not well acquainted with them. Only those who have a very good knowledge of the Sanskrit language and who have been directly initiated by a Guru (who has Mantra-Siddhi) can take up the Japa of Bija-Mantras and the Sri-Vidya. Others should not approach these Mantras and should do only their own Ishta-Mantras which are easy to pronounce and remember.
Mantra-Meditation (Swami Vishnudevananda)
"I hereby state and fully affirm that any Bija mantras or alleged Bija mantras used
by the various organizations have been in public domain
for centuries. They are commonly known in India and parts of the west. They can
be located in books which I and other authors have published and can be found in
almost any free library.
Many of the Bija Mantras are listed in my book, " Meditation and Mantras ".
My Guru, H.H. Swami Sivananda of Rishikesh, listed these mantras in his work, "Japa Yoga" in the section on Bija Mantras.
The effortless, passive repetition of these mantras is not unique to the practice of the defendants programs,and is common in all meditative practices.
Here I guote points 8 and 9 from the 14 points of meditation outlined in Chapter2 of my book, "Meditation and Mantras":
8. Allow the mind to wander at first. It will jump around, but will
eventually become concentrated, along with the concentration of prana.
If an individual who is unqualified or unprepared to begin meditation uses a bija mantra, negative physiological or psychological effects can occur.
The Yoga sutras of Patanjali and the practice of the formulas which result in siddhis are common practices taught throughout India. Many translations of the Yoga Sutras can be found in many libraries throughout the world. The Raja Yoga sutras have also been introduced to my students through my book "Meditation and Mantras" as taught by my own Guru, Swami Sivananda. Further the goal of Yoga is not the obtainment of siddhis, and these powers are not to be sought as an end in themselves. Patanjali himself warns in chapter 3 of the Raja Yoga Sutras:
(37.) From that comes intuitional hearing, thought, sight taste and smell.
38. Te samadhau upasarga vyutthane siddhayah:
Patanjali makes it clear that the siddhis described above are but temptations and distractions from the superconscious state. They only appear attractive to those who are steeped in worldliness, egoism and the desire for power. Seeking these powers can bring many physiological and psychological problems to the individuals concerned.
Translations of the Rig Veda - Mandalas 1 thru 10 and translations of the Jaimini Sutras are not the private, unique secret information of any particular organization, but rather are part of the scripural heritage of India and are commonly known and publicly used.
The information regarding the mantras, techniques and scriptural books listed above are most definitely not a copywritable unique body of knowledge , nor are they the trade secrets of the defendants various organizations. Rather they are an integral part of the rich cultural and scriptural heritage which belongs to India.
[30. June 1986]
[Om Namo Narayanaya...Om-Peace-Om Santi]
(P.S. The part about the siddhis only for completeness. A true godseeker avoids these forces as Sri aurobindo said too).