Japa, The age-old Method of Meditation
It can be said that the Western world got initiated en-mass, into meditation in modern times through Transcendental Meditation (T.M. aspopularized by Maharshi Mahesh Yogi).
Transcendental Meditation is just a new name given to the ancient art (and science) of meditation-Japa. The great sage Narada proclaims "Japa is the only way to salvation in Kaliyuga". Japa: repetition of a mantra, a sabda, a nama whatever be the term, it means a sound. Mantra-ghosha is a great science in itself. From times immemorial sages and saints have prescribed Japa to the devotees forsadhana. It ancient times sage Narada's prescription of the Mantra "Om Namo Bhagvate Vasudevayah" to child Dhruva is a famous story. In modern times one of the masters to lay theemphasize on Japa is the founder of Sikhism, Guru Nanak Deo.
One may begin repetition of a mantra verbally or mentally but slowly after a long practice as various levels of consciousness gets unfolded, he arrives at the core, the subtlest part of the mantra.
A time comes when Japa is not 'done', it happens, it becomes automatic, it keeps on going on its own. Some call it 'Ajapa-Japa'. Great Devotee Hanuman's each and every cell in his body used to reverberate with the sacred mantra "Ram". In modern times, one of the friends of Swami Rama Tirtha could hear in mind-night, the sound "Ram-Ram" emanating from his entire body.
According to Yogic science, a mantra becomes a vehicle tochannelize the energy, the untamed forces of our mind. Gradually we descend in deep silence and profound peace when the mantra dissolves in nothingness. It can be any mantra. May be, a mathematician may like to just repeat "Triangle, triangle, triangle...." etc. It will help him, as mentioned above, to withdraw his mind from multiple thoughts and lead him to a 'no-thought' state rituals or no rituals.
While some people associate unnecessary myths and inhibitions with 'Japa', some others (the so called progressive nationalists and psychologists etc) have fears of different kind. They feel, for example, repetition of a mantra makes our mind dull. The scientific experiments have shown that Japa enhances our physical and mental health.
Mantra for the Japa can be long or short depending on the nature of the mental state of a sadhaka. For example, for a restless mind a long mantra (may be verbal chanting) would be suitable. Whereas for a sattvic person, mental repetition of a mantra with a single syllable will do. The sacred mantra OM is prescribed even for Sanyasins who have renounced all.
Omkar Dhyana taught in various camps conducted by Vivekananda Kendra helps many participants to get into the sublime states of mind.