Japa (repetition of the name of God) is considered to be one of the easiest and most efficacious means of attaining spiritual illumination. Lord Kṛṣṇa goes to the extent of identifying himself with it and calls it a yajña or sacrifice (Bhagavadgītā 10.25). When japa is practised constantly and continuously, practically with every breath, it gets merged as it were with the process of breathing itself. Such an unconscious and automatic japa is christened ‘ajapā-japa.’
Though theoretically, any mantra pertaining to any deity can be chosen for this purpose, in practice this is always confined to the ‘haṁsamantra.’ ‘Haṁsaḥ’ is the abbreviation of ‘ahaṁ saḥ’ (‘I am He’) or its more well-known form “so’ham” (‘He, I am’). With every inhalation the syllable ‘haṁ’ is repeated and with every exhalation the syllable saḥ. Deliberate and conscious practice of this will gradually result in automatic and unconscious repetition coeval with breathing. It is only then that it becomes ‘ajapājapa.’
“Haṁ-saḥ” or “so’ham” is actually the same as the mahāvākyas (the great dicta of the Upaniṣads—See MAHĀVĀKYAS for details.) aham brahma asmi (‘I am Brahman’) or tat tvam asi (‘You are That’). In these statements ‘aham’ or ‘tvam’ represents the jīva or the individual soul; ‘brahma’ or ‘tat’ stand for the Supreme Soul or the Absolute. Since the two are apparently poles apart, they can never be identical. However, when only their essential characteristic, viz., caitanya or pure consciousness is considered, they can be considered identical or as the same.
According to the Tantras, ‘ham’ repre-sents the Śiva principle and ‘saḥ’ represents the Śakti principle. So ‘haṁsaḥ’ stands for their union and the entire universe created from that union.
Literally haṁsa means a swan. Swan is the vehicle of Brahmā the creator. Haṁ and saḥ represent the inspired and expired breath. Everything movable and immovable “breathes” or vibrates and hence can be denoted by ‘haṁsa.’ Therefore it is meet that Brahmā the creative aspect of the Supreme Self is represented as seated thereon.
The Haṁsopaniṣad (15) describes the cosmic form of God using the haṁsa imagery to facilitate meditation. The same Upaniṣad also relates the experiences that arise as a result of the ajapājapa of haṁsa-mantra (16).
Repetition of the haṁsa-mantra or ajapājapa is also known as Ajapāhaṁsa-vidyā.