There is another excerpt from Gurudev's book Japa Yoga at the TM web site. It explains the meaning of the Bija-Akshara (seed letters such as Om, Kleem, Gam, etc.). Click here to read that article.

WHAT IS JAPA ?

Repetition of any Mantra or Name of the Lord is known as Japa. Japa is an important Anga of Yoga. It is a spiritual food for the hungry soul. Japa is the rod in the hand of the blind Sadhakas (aspirants) to plod on the road to Realization. Japa is the philosopher's stone or divine elixir that makes one God-like. In this iron age, practice of Japa alone can give eternal Peace, Bliss and Immortality.

Japa is repetition of the Mantra. Dhyana is meditation on the form of the Lord with His attributes. There is meditation or Dhyana with Japa (Japa-Sahita-Dhyana); there is meditation or Dhyana without Japa (Japa-Rahita-Dhyana). In the beginning you should combine Dhyana with Japa. As you advance the Japa drops by itself; meditation only remains. It is an advanced stage. You can then practice concentration separately. You can do whatever you like best in this respect.

Name (Nama) and the object (Rupa) signified by the Name are inseparable. Thought and word are inseparable. Whenever you think of the name of your son, his figure stands before your mental eye, and vice versa. Even so when you do Japa of Rama, Krishna or Christ, the picture of Rama, Krishna or Christ will come before your mind. Therefore Japa and Dhyana go together. They are inseparable.

Do the Japa with feeling. Know the meaning of the Mantra. Feel God's presence in everything and everywhere. Draw closer and nearer to Him when you repeat the Japa. Think He is shining in the chambers of your heart. He is witnessing your repetition of the Mantra as He is the witness of your mind.

MANTRA

'Mananat-trayate iti Mantrah' - By the Manana (constant thinking or recollection) of which one is protected or is released from the round of births and deaths, is Mantra. That is called Mantra by the meditation (Manana) on which the Jiva or the individual soul attains freedom from sin, enjoyment in heaven and final liberation, and by the aid of which it attains in full the fourfold fruit (Chaturvarga), i.e., Dharma, Artha, Kama and Moksha. A Mantra is so called because it is achieved by the mental process. The root 'Man' in the word Mantra comes from the first syllable of that word, meaning 'to think', and 'Tra' from 'Trai' meaning 'to protect' or 'free' from the bondage of Samsara or the phenomenal world. By the combination of 'Man' and 'Tra' comes Mantra.

A Mantra is divinity encased within a sound-structure. It is divine power or Daivi Sakti manifesting in a sound-body. The Mantra is itself Devata.

The sacred Mantra or the Divine Name is a vital symbol of the Supreme Divinity directly revealed in the innermost depths of divine communion to the sages of Self-realization in the hoary Vedic and Upanishadic times. These symbols are in the nature of unfailing keys to gain access into the transcendental realms of absolute experience.

Mantra Yoga is an exact science. A Mantra, in the Hindu religion, has the following six parts. It has got a Rishi (a man of Self-realization) to whom it was revealed for the first time and who gave this Mantra to the world. He is the Drashta or Seer for this Mantra. Sage Viswamitra is the Rishi for Gayatri. Secondly, the Mantra has a metre (Chhandas), which governs the inflection of the voice. Thirdly, the Mantra has a particular Devata or supernatural being, higher or lower, as its informing power. This Devata is the presiding deity of the Mantra. Fourthly, the Mantra has got a Bija or seed. The seed is a significant word, or series of words, which gives a special power to the Mantra. The Bija is the essence of the Mantra. Fifthly, every Mantra has got a Sakti. The Sakti is the energy of the form of the Mantra, i.e., of the vibration-forms set up by its sound. These carry the man to the Devata that is worshipped. Lastly, the Mantra has a Kilaka - pillar or pin. This plugs the Mantra-Chaitanya that is hidden in the Mantra. As soon as the plug is removed by constant and prolonged repetition of the Name, the Chaitanya that is hidden is revealed. The devotee gets Darshana of the Ishta Devata.

SOUND AND IMAGE

Sounds are vibrations. They give rise to definite forms. Each sound produces a form in the indivisible world, and combinations of sound create complicated shapes. Repetition of a Mantra has a mysterious power of bringing about the manifestation of the Divinity, just as the splitting of an atom manifests the tremendous forces latent in it. When a particular Mantra appropriated to a particular god is properly recited, the vibrations so set up create in the higher planes a special form which that god ensouls for the time being. The repetition of the Panchakshara Mantra - Om Namo Sivaya - produces the form of Lord Siva. The repetition of Om Namo Narayanaya, the Ashtakshara Mantra of Vishnu, produces the form of Vishnu.

GLORY OF DIVINE NAME

The Name of God, chanted correctly or incorrectly, knowingly or unknowingly, carefully, is sure to give the desired result. Just as burning quality is natural to and inherent in fire, so also, the power of destroying sins with their very root and branch, and bringing the aspirant into blissful union with the Lord through Bhava-Samadhi, is natural to and inherent in the Name of God.

The glory of the Name of God cannot be established through reasoning and intellect. It can be experienced or realized only through devotion, faith and constant repetition of the Name.

There is a Sakti or power in every word. If you utter the word 'excreta' or 'urine' when your friend is taking his meals, he may at once vomit his food. If you think of 'Garam Pakoda', 'hot Pakoda' (fried delicacies), your tongue will get salivation. When anyone suddenly shouts 'Scorpion! Scorpion!', 'Snake! Snake!', you at once apprehend the scorpion or the snake and jump in fright. When anyone calls you a 'donkey' or an 'ass', you are annoyed and you show anger. If anyone says, "You are a nice person," you smile. When such is the power of the names of the ordinary things of this world, what tremendous power should there be in the Name of God! God is the completion or the fullness of existence. Hence, the Name which denotes Him, too, is full and perfect. Therefore, the power of the Name of God is incalculable, for it is the height or the zenith of power. The Name of God can achieve anything. There is nothing impossible for it. It is the means to the realization of God Himself. Even as the name of a thing in this world generates the consciousness of that thing in the mind, the Name of God generates God-consciousness in the purified mind and becomes the direct cause of the realization of the Highest Perfection or God.

VARIETIES OF JAPA

Repeat the Mantra verbally for sometime, in a whisper for sometime, and mentally for sometime. The minds wants variety. It gets disgusted with any monotonous practice. The mental repetition is very powerful. It is termed Manasika Japa. The verbal or loud repetition is called Vaikhari Japa. The loud Japa shuts out all worldly sounds. There is no break of Japa here. Repetition in a whisper or humming is termed Upamshu Japa. Even mechanical repetition of Japa without any Bhava has a great purifying effect on the heart or the mind. The feeling will come later on when the process of mental purification goes on.

Write down daily in a notebook your Ishta Mantra or Guru Mantra for half an hour. When you write the Mantra, observe Mouna. Write the Mantra clearly in ink. On Sundays and holidays, write this for one hour. This is Likhita Japa You can develop a wonderful power of concentration.

The benefits of Mantra-writing or Likhita Japa cannot be adequately described. Besides bringing about purity of heart and concentration of mind, mantra-writing gives you control of Asana, control of Indriyas, particularly the sight and the tongue, and fills you with the power of endurance. You attain peace of mind quickly. By prolonged and constant practice the inherent power of the Mantra (Mantra-Sakti) will be awakened, which will fill your very existence with the Divinity of the Mantra.

In Mantra writing, there is no restriction about any particular script. It may be written in any language.

PRACTICAL AIDS TO JAPA

Select any Mantra or Name of God, preferably that given to you by your Guru, and repeat it from 108 to 1,080 times daily (one to ten malas).
Always keep your Guru-Mantra a secret. Never disclose it to anyone.
It is better to stick to one Mantra only. See Lord Krishna in Rama, Shiva, Durga, Gayatri and in everyone.
Get up at 4a.m. and do Japa for two hours. The early morning period (Brahmamuhurta) and dusk is the most favourable time for Japa and meditation. This is when Sattva (purity or steadiness) is predominant.
Take a bath or wash your hands, feet, face and mouth before sitting for Japa in the morning. At other times this is not absolutely necessary. Do Japa whenever you have leisure, at the three junctions of the day - morning, noon and evening - and before going to bed.
Face east or north during the practice. This enhances the efficacy of the Japa. Sit on a deer skin or rug. Spread a piece of cloth over it. This conserves body-electricity. Sit in a separate meditation room or in any suitable place, such as a temple, on a river bank or under a banyan or peepul tree.
Maintain a steady pose. Attain mastery of the posture. You must be able to sit in Padmasana, Siddhasana or Sukhasana for three hours at a strech.
Reslove to complete a certain minimum number of malas before leaving your seat.
Recite some prayers before starting the Japa.
A rosary is a whip to goad the mind towards God. Use a rudraksha or tulsi mala of 108 beads.
Do not allow the mala to hang below the navel. Keep the hand near the heart or the nose.
The mala must not be visible to you or to others. Cover it with a towel or handkerchief, which must be clean and washed daily.
Use the middle finger and the thumb of the right to roll the beads. The use of the index finger is prohibited.
Do not cross the meru while rolling the beads. Turn back when you come to it.
Sometimes do the Japa without a mala. Use a watch.
Do mental Japa for a time. When the mind wanders, do the Japa aloud, or whisper the Mantra for some time and come back to mental Japa again as soon as possible.
When you repeat the Mantra, have the feeling or mental attitude that the Lord is seated in your heart, that purity or Sattva is flowing from the Lord into your mind, that the Mantra is purifying your heart, destroying desires, cravings and evil thoughts.
Do not do the Japa in a hurried manner, like a contractor who tries to finish his work in a short time. Do it slowly with feeling, one-pointedness of mind and single-minded devotion.
Pronounce the Mantra distinctly and without any mistakes. Repeat it neither too slowly nor too fast. Increase the speed only when the mind wanders.
Be vigilant and alert during Japa. Stand up when sleep tries to overpower you.
Try to associate the Japa with the rhythm of the breath and meditate in the form of your Deity. Keep a picture or idol of the Deity in front of you. Think of the meaning of the Mantra while repeating it.
Regularity in Japa Sadhana is most essential if success is to be achieved. Sit in the same place and at the same time every day.
Do not beg for any worldly objects from God while doing Japa. Feel that your heart is being purified and that the mind is becoming steady by the power of the Mantra and the Grace of the Lord.
Observe silence and avoid distractions, calls and engagements.
It is important not to leave the place at once after the Japa is over and mix with everyone or plunge into worldly activity. Sit very quietly for at least ten minutes, humming some prayer, remembering the Lord and reflecting upon His infinite love. Then, after devout prostration, leave the place and commence your routine duties and activities. In this way the spiritual vibrations will remain intact.
Continue the current of Japa mentally at all times, whatever be the activity in which you are engaged. Carry on your Sadhana with tenacity and perseverance, without a break. Realize the glorious goal of life and enjoy supreme bliss.

MANTRAS FOR JAPA

Lord Krishna:
- Maha-Mantra :
  Hare Rama Hare Rama
  Rama Rama Hare Hare
  Hare Krishna Hare Krishna
  Krishna Krishna Hare Hare
- Om Namo Bhagavate Vasudevaya
- Om Sri Krishnaya Govindaya Gopijana Vallabhaya Namah
- Om Sri Krishnaya Namah
Sri Devi:
- Om Sri Durgayai Namah
Lord Ganapati:
- Om Sri Ganapataye Namah
Sri Hanuman:
- Om Sri Hanumate Namah
Lord Hari:
- Om Namo Narayanaya (Ashtakshara)
- Hari Om
- Hari Om Tat Sat
Jugal (Combined) Mantra:
- Sita Ram
- Radhe Shyam
- Radhe Krishna
Sri Kalika:
- Om Sri Kalikayai Namah
Sri Lakshmi:
- Om Sri Maha-Lakshmyai Namah
Lord Shiva:
- Maha-Mrityunjaya Mantra:
  Om tryambakam yajamahe
  sugandhim pushtivardhanam
  uurvarukamiva bandhanaan
  mrityor mukshiya maamritaat.
- Om Namah Shivaya (Panchakshara)
Lord Rama:
- Om Sri Ram Jaya Ram Jaya Jaya Ram
- Om Sri Ramaya Namah
- Sri Rama Rama Rameti,
  Rame Rame Manorame
  Sahasranama Tattulyam Rama Nama Varanane
- Om Sri Sita-Ramachandradhyam Namah
- Sri Ram
Sri Saraswathi:
- Om Sri Sarasvatyai Namah
Lord Subramanya, Kartikeya:
- Om Sri Saravanabhavaya Namah
Sharangati Mantra (for surrender):
- Om Sri Ramah Sharanam Mama
- Om Sri Krishnah Sharanam Mama
- Om Sri Sita-Ramah Sharanam Mama
Sharada:
- Om Sri Bala-Parameshvaryai Namah
Tripurasundari:
- Om Sri Tripura-Sundaryai Namah
Vedantic Formulae:
- Om Soham
- Om Tat Tvam Asi
- Om Aham Brahma Asmi