The need for exercise is perhaps less obvious, but is certainly not less urgent.

We make our limbs, our organs, our senses, our faculties grow by exercising them.

When they have reached their maximum of development we maintain them at that level by exercising them.

When their capacity for growth is unlimited, as in the case of our mental and spiritual faculties, the need for exercise is still more urgent.

To neglect to exercise a given limb, or organ, or sense, or faculty, would result in its becoming weak, flabby, and in the last resort useless.