Those are the only words which are suitable for Mantra or Japa Yoga. A Mantra is divinity encased within a sound structure. It is Divine Power or Daivi Sakti manifesting in a sound body. . . The Sacred Mantra or the Divine Name is the 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.
Sounds are vibrations.
They give rise to definite forms. Each sound produces a form in the invisible world and combination of sounds create complicated shapes. I have stressed emphatically that the Name is a Sacred Force. Even if you repeat it automatically. Yet there should be an inner background for it.