“Every inferior is governed by its superior, and receiveth the influence of the virtues thereof.”
Virtues are influences inherent in something because of hierarchies in the occult cosmology.
When one says that a stone or herb has a certain power they are in fact referring to the virtue. In the western system of Occultism the virtue is almost always quantified with the hierarchical relationship between the Elements, the Planets, or the Zodiac. This stems from the Neo-Platonic, or more directly hermetic, belief that the material universe is ordered to reflect the influence of its superior counterpart in the celestial or spiritual realm.
As an example Agrippa describes that God, in the singular, delegates to the angels, who move the heavens the stars, the elements, animals, plants, metals, and stones, to enact the virtues of the almighty on the earth.
He further reasons that via this chain of influence:
“Wise men conceive it no way irrational that it should be possible for us to ascend by the same degrees through each world, to the same very original world itself, the Maker of all things, the first cause, from whence all things are, and proceed.”
This is the basic principle of Theurgy , or spiritual development via magic, in western ceremonial magic.