What sounds from his mouth, is not the ordinary word, the shabda, of which speech is composed. It is mantra, the compulsion to create a mental image, power over that which IS, to be as it really is in its pure essence.
Govinda distinguishes mantra from ordinary speech as a primal creative force that commands reality at the level of pure essence rather than conventional designation.
, Foundations of Tibetan Mysticism, 1960thesis