Walter Wink’s book The Powers That Be (Doubleday 1998) gives some very interesting insights into Christians’ spiritual battle against evil powers. I don’t endorse everything in the book, as the underlying theology is somewhat “liberal”; for example, Wink writes (p.197):

I do not believe that evil angels seize human institutions and pervert them. Rather, I see the demonic as arising within the institution itself, as it abandons its vocation for a selfish, lesser goal.

But I was struck in a positive sense by this paragraph, the start of chapter 10 “Prayer and the Powers” (p.180):

Every dynamic new force for change is undergirded by rigorous disciplines. The slack decadence of culture-Christianity cannot produce athletes of the spirit. Those who are the bearers of tomorrow’s transformation undergo what others might call disciplines, but not to punish themselves or to ingratiate themselves to God. They simply do what is necessary to stay spiritually alive, just as they eat food and drink water to stay physically alive. One of these disciplines, perhaps the most important discipline of all, is prayer.

And in the last paragraph of the chapter (pp.197-198) he writes:

In a field of such titanic forces, it makes no sense to cling to small hopes. We are emboldened to ask God for something bigger. The same faith that looks clear-eyed at the immensity of the forces arrayed against God is the faith that affirms God’s miracle-working power. Trust in miracles is, in fact, the only rational stance in a world that can respond to God’s incessant lures in any number of ways. We are commissioned to pray for miracles because nothing less is sufficient. We pray to God, not because we understand these mysteries, but because we have learned from our tradition and from experience that God, indeed, is sufficient for us, whatever the Powers may do.