In traditions that use a subtle-body framework, sound is not an accompaniment to practice but a component of it. The reasons are visible in how mantras are prescribed and used.
Vibration is treated as operative
These traditions hold that sound acts rather than merely signifies, and mantras are consequently specified by exact syllable, pronunciation and repetition rather than by meaning alone.
Many prescribed formulas have little or no translatable content, which makes sense if the sound itself is what the practice depends on.
The insistence on precise pronunciation follows from the same premise, and it explains the elaborate phonetic training attached to recitation in several lineages.
Sound is produced in the body
Chanting involves breath, throat, palate and chest, and a sustained tone is felt physically in the head and torso by anyone producing it.
That felt vibration is directly available, which gives practitioners something concrete to attend to when instructions refer to locations within the body.
Practices that pair specific syllables with specific regions rely on this, using an audible and palpable sensation to direct attention precisely.
Repetition holds attention without content
A repeated formula occupies the verbal capacity that would otherwise generate commentary, which is a large part of what makes concentration difficult.
Because the syllables carry no ordinary meaning to follow, the mind has less to elaborate on than it would with a phrase in the practitioner's own language.
The rhythm also links naturally to breath, so the practice tends toward a stable cycle once it has been running for a while.
Transmission is often restricted
Many lineages give particular mantras only to particular students, sometimes privately, and treat the giving as a formal step within a longer relationship.
The practice serves practical purposes, ensuring correct pronunciation and appropriate timing, and it also marks the formula as belonging to a chain of transmission rather than to a book.
Because these conventions differ between traditions and are taken seriously within them, printed collections of mantras sit awkwardly with how the material is meant to be handled.
Collective chanting does something additional
Group recitation synchronises breathing and produces a sustained sound larger than any participant contributes, which participants across many traditions describe consistently.
The effect requires no explanation beyond what is observable, and it is one reason communal chanting appears in traditions that share no theory of sound at all.
Where a subtle-body framework is present, that shared experience is interpreted within it, which is how a widespread practice acquires a tradition-specific meaning.