Clerics are among those who associate closely with the spirits of the world. Through close relations with the spirits, a cleric understands nuances of the spirits' nature more clearly than others. They see how spirits represent and affect the world they manifest from, and because of this are able to act as the spirits do to affect the world in similar ways.
Often, a cleric has a spirit mentor or family of spirits to learn from. Especially enlightened clerics often take up the instruction of lesser spirits, who may rise to higher forms through such intervention, and may have an entourage of spirits both teaching and learning from them.