मनःप्रसादः सौम्यत्वं मौनमात्मविनिग्रहः।भावसंशुद्धिरित्येतत्तपो मानसमुच्यते॥
manaḥ-prasādaḥ saumyatvaṃ maunam ātma-vinigrahaḥbhāva-sanśuddhir ity etat tapo mānasam ucyate
Word by word
The verse says
A settled mind, gentleness, quiet, keeping yourself in hand, and being clean through and through - this is called the discipline of the mind.
In plain words
Five, and the middle one is the odd one.
Mauna - silence. Not merely not speaking. The older sense is the quiet of somebody who does not need to put in a word.
And it sits between gentleness and self-command, which is exactly right. Most unnecessary speech is neither kind nor controlled. It is pressure finding a gap.
Where you've felt this · in study
There is someone in every group who does not speak for the first twenty minutes of a discussion. People assume at first that he has nothing. Then he says one thing near the end and the whole conversation reorganises around it. He was not holding back for effect. He simply had no need to be heard until he had something.
Going deeper
Silence as a discipline of the mind rather than of the mouth is what is being named here.
Mauna is usually rendered silence and read as a vow not to speak. The sense here is wider. It is the condition of a mind that is not under pressure to be heard. The mouth stays shut as a consequence, not as an effort.
That is why it is filed with gentleness and self-command rather than with speech. Forced silence is suppression with a clock on it, and anybody nearby can feel it. A quiet person who is straining is not restful to be near.
And the first item tells you the order. A settled mind comes first and the quiet follows from it. Which is the reverse of how people usually attempt this - enforcing the silence and waiting for the settling to turn up.