Mantra virya
The classic Tantric tradition referred to itself as the mantra marga (the way of mantra).
They believed that the mantra provided a much faster path to liberation. The reason for this can be found in their thoughts about what a mantra, and not only a mantra, but also what a word, is.
They had realised that our worldview is ultimately shaped by our words or other symbols such as images. It is these that give demarcation and the possibility to term or think separate things.
They divided the word into four different levels:
Vaikhari vac-The spoken word.
Madhyama vac-The word of thinking.
Pashyanti vac- The wordless word. This is what in psychoanalysis is called the unconscious.
Para vac- The original word, the essence of all things being, the nature of which is a vibration.
In all the practice of Yoga, you finally want to get to the deepest, last of these levels. The direct, representationless experience of reality and ourselves.
So even in mantra practice, one goes from the spoken word to the intended word, to the wordless word, to the experience of the underlying vibration.
It is this last form of mantra practice that is considered especially potent. And when a mantra was experienced at this level, it was also considered able to be transferred as a vibration to someone else.