The set-aside Power Card is being "played" by the previous Spirit, and the special rules of that Spirit are in effect. The Power acts as if the previous Spirit has a Sacred Site in every land. The previous Spirit is shown on the artwork of the Power Card. In the example below, it was A Spread of Rampant Green.

For example, if the previous Spirit was Bringer of Dreams and Nightmares, then the power cannot damage or destroy anything, and generates fear/pushes according to that Spirit's special rule.