Chanting in yoga was and is a means of carrying the knowledge down through the ages. When we write thing down, we deal with external forms and is perceived as the grossest level of interpretation of oral traditions. When we chant we use our vocal apparatus to produce the sound. This process brings us into the eternal or” Now”. When we write, a time lapse of time can pass between time of writing and our re reading.
All mantra can be chanted in three forms, The Vachika form(chanting externally, uttering sound) is between the likita(written) and the subtlest way of approach would be to chant them in our mind. Yet this requires full knowledge in what one is doing a yoga sutra.
When we chant, the action brings us in the present moment, as the process of chanting demards full attention, at least on a physical level. There’s is also the question of resonance or sound vibration through our cell and beyond.
Chanting evokes and invokes an universal resonance in the words.