"Herbs are the finest energy of mountains and streams, the essential florescence of grasses and trees. They may be warm, or they may be cool; one uses them to supplement or drain energy. They may be thick, or they may be thin; one uses them externally or from within.
Studying herbs in their essence allows you to support your inner nature and destiny. On the other hand, if you apply herbs blindly, you will waste your body and physical constitution.
All those who study the Tao must penetrate herbal lore. If you do not do so, you have no means to support the Tao. Yet in doing so, you must not develop attachments, for they will diminish the hidden merits of past lives. You will hanker after material goods on the outside and waste your efforts at cultivation within.
Not only does this lead to grave transgressions and errors in this life, but it will also cause retribution in the lives to come. Oh, noble disciples of my teaching! Head this and be very careful!"
- page 88 of The Taoist Experience - An Anthology edited by Livia Kohn