They do not clearly see how these words can act on the mind. It is true, in a certain way, that words are only sounds getting lost in space. Nevertheless, they are vectors of great power. This power is obvious even in daily situations. In a way, meditation should arouse even more doubts than mantras.
Reticence concerning the recitation of mantras comes from two factors.
Kalu Rinpoche, a lama of the Shangpa Kagyu lineage, was born in Eastern Tibet in 1904. He studied and practiced with many great beings of all traditions before living in solitary retreat for 12 years. One of the first Tibetan masters to teach in the West, he passed away in 1989.