Sri Aurobindo
Letters of Sri Aurobindo
Volume I - Part 2
The vital mind is usually energetic and creative even in its more mechanical rounds, so it must be the physical that is turning. It is that and the mechanical that last longest, but these too fall silent when the peace and silence become massive and complete. Afterwards knowledge begins to come from the higher planes – the Higher Mind to begin with, and this creates a new action of thought and perception which replaces the ordinary mental. 
It does that first in the thinking mind, but afterwards also in the vital mind and physical mind, so that all these begin to go through a transformation. This kind of thought is not random and restless, but precise and purposeful – it comes only when needed or called for and does not disturb the silence. Moreover the element of what we call thought there is secondary and what might be called a seeing perception (intuition) takes its place. But so long as the mind does not become capable of a complete silence, this higher knowledge, thought, perception either does not come down or, if partially it does, it is liable to get mixed up with or imitated by the lower, and that is a bother and a hindrance. So the silence is necessary.