Etymologically, the term “Mantrayana” may be explained as follows. In Sanskrit, “mantra” is a conflation of the elements “manas,” which means “mind,” and “traya,” which means “to protect.” In other words, mantra is a protection for the mind. This mind is also described as awareness (rig pa), or, speaking in terms of the result, as self-cognizing primordial wisdom (rig pa’i ye shes). As it is said in the Guhyagarbha-tantra (the Tantra of the Secret Essence): “The Bhagavan Creator is the vajra mind, Samantabhadra.” And if one were to ask from what it is that mantra protects us, the answer is that it protects from the eight kinds of consciousness, which are marred by the duality of subject and object. And as for the kind of protection that mantra affords, it is a protection that is swift and easy.
Treasury of Precious Qualities: Book Two