The mind commands the body and it obeys.
Augustine has obviously never tried to learn something which requires complicated movement, or at least he didn't try it as an adult.
The general principle is: cached is fast, cache-populating is slow. This goes for mind and "body" both, because the body does as its told, but it needs telling in a lot of detail and the control signals need to be discovered. Most people, for both mind and body, learn enough control signals for day-to-day use, and stop.
I do somewhat wonder what it would be like to know the control signals for all my muscles, Bene Gesserit style.
Here's the new thread for posting quotes, with the usual rules: