In various cultures, there is the concept of a “spiritual intermediary” human between this world and that world.

Probably I understood what is the issue:

Apparently, the powerful outer space spirits (cosmic plasma) and spirits here on the Earth act on different electromagnetic frequencies. To control earthy spirits, heavenly spirits may need a retranslator on the Earth. And a human brain can serve as this retranslator.

So, if this concept is true, heavenly spirits control earthy spirits trough humans. This explains how humans could participate in spiritual wars despite being spiritually weak by themselves.