Human body is like a horse which carries the personality and spirit

... you should not neglect your health, but consider it the means which enables you to serve. It - the body - is like a horse which carries the personality and spirit, and as such should be well cared for so it can do its work! You should certainly safeguard your nerves, and force yourself to take time, and not only for prayer and meditation, but for real rest and relaxation. 

- Shoghi Effendi  (From a letter dated November 23, 1947 written on behalf of Shoghi Effendi to an individual believer; printed in compilation: ‘Spiritual Foundations’)