Whatever we are doing we can make use of the between times to rest.

Each man can find his own "between times." If we make real use of them, intelligent use, they not only help us to keep rested, they help us to do our work better, if we will but watch for them and use them.
Now the body is only a servant, and in all I have written above, I have only written of the servant.

How can a servant keep well and rested if the master drives him to such an extent that he is brought into a state, not where he won't go, but where he can't go, and must therefore drop?
It is the intelligent master, who is a true disciple of plain common sense, who will train his servant, the body, in the way of resting, eating and breathing, in order to fit it for the maximum of work at the minimum of energy.

But if you obey every external law for the health and strength of the body, and obey it implicitly, and to the letter, with all possible intelligence, you cannot keep it healthy if the mind that owns the body is pulling it and twisting it, and _twanging_ on its delicate machinery with a flood of resentment and resistance; and the spirit behind the mind is eager, wretched, and unhappy, because it does not get its own way, or elated with an inflamed egoism because it is getting its own way.
All plain common sense in the way of health for the body falls dead unless followed up closely with plain common sense for the health of the mind; and then again, although when there is "a healthy mind in a healthy body," the health appears far more permanent than when a mind full of personal resistance tries to keep its body healthy, even that happy combination cannot be really permanent unless there is found back of it a healthy spirit.
But of the plain common sense of the spirit there is more to be said at another time.
With regard to the mind, let us look and see not only that it is not sensible to allow it to remain full of resistance, but is it not positively stupid?
What an important factor it should be in the education of children to teach them the plain common sense needed to keep the mind healthy--to teach them the uselessness of a mental resistance, and the wholesomeness of a clean mind.
If a child worries about his lessons, he is resisting the possibility of failing in his class; let him learn that the worry _interferes_ with his getting his lesson.

Teach him how to drop the worry, and he will find not only that he gets the lesson in less time, but his mind is clearer to remember it.
By following the same laws, children could be taught that a feeling of rush and hurry only impedes their progress.