We live in a realm of sound and vibration. In the Indian system of thought, space and ether are related to sound. When in need of more room for ourselves, or when lost, we turn to sound. In yoga technique, a central practice of this is mantra. But if you are not into yoga, apply everything I say to singing. It will also work.
Mantra’s etymology comes from man— (related to the mind) and —tra(instrument). But the translation is complicated because Sankrit has denotations and connotations. It is an instrument for the mind, a transforming idea which ‘when thought, carries one across [the worldly ocean of sorrow]’ (‘mananaath thraayathe’). But man— also relates to sound, space, jewels, heart, intelligence, devotion and —tra is linked to shining, speaking and protecting. So, a mantra is an instrument that protects the mind from confusion. A mantra is the function of the mind which, speaking intelligently, shines like a jewel.
A mantra is simply a series of powerful sounds that can produce a particular physical or psychological effect, not just something that has an assigned intellectual meaning. The power of a mantra lies in its ability to produce an objective, perceptible change in the yogi who repeats it correctly (and precision is, to a certain extent critical, although sincerity is paramount).
The energies we invoke through mantra are important to bear in mind. If you constantly sing to Kali, you need to be prepared for deep and complete transformation to happen. I have my favourites, of course, but I also try to balance their energies. Change might be needed, but also beauty and nurture and compassion. Ganesa (Gaṇeśa Śaraṇaṁ Śaraṇaṁ Gaṇeśa Oṁ Gaṁ Gaṇapataye namaḥ), the harmonising energy of the gang working together, is one I constantly return to. And as I practice Ashtanga Yoga, I open each morning with Vande Gurunam. David Swenson translates this mantra in a really simple way: the rishis (seers, wise people) are coming! This is a good way of feeling beneath the language: we are invoking the energy of those who have been there before us so they can help us and keep us company on the path.
Mantra also has a connotation of the secret and it is not uncommon for a mantra to be given to you personally, which you should never reveal. Mantra is one of the most powerful tools I know and practice. Subtle, but like any vibration repeated, it can tear anything down. It helps to see clearly and resolve knots, offers space and heals through sound.