Changes

The stillness of the mind means, first, the falling to rest of the habitual thought movements, thought formations, thought currents which agitate this mind-substance. That repose, vacancy of movement, is for many a sufficient mental silence. But, even in this repose of all thought movements and all movements of feeling, one sees, when one looks more closely at it, that the mind-substance is still in a constant state of very subtle formless but potentially formative vibration—not at first easily observable, but afterwards quite evident—and that state of constant vibration may be as harmful to the exact reflection or reception of the descending Truth as any formed thought movement or emotional movement… When I speak of a still mind, I mean then one in which these subtler disturbances too are no longer there. As they fall quiet one can feel an increasing stillness which is not the lesser quietude of repose and also a resultant clearness as palpable as the stillness and clearness of a physical atmosphere.

<ref>http://incarnateword.in/cwsa/28/philosophical-thought-and-yoga#p17</ref>

... in the calm mind, it is the substance of the mental being that is still, so still that nothing disturbs it. If thoughts or activities come, they do not rise at all out of the mind, but they come from outside and cross the mind as a flight of birds crosses the sky in a windless air. It passes, disturbs nothing, leaving no trace. Even if a thousand images or the most violent events pass across it, the calm stillness remains as if the very texture of the mind were a substance of eternal and indestructible peace.

<ref>https://incarnateword.in/cwsa/29/quiet-and-calm#p56</ref>