"'Behold, I am not Gandalf the Grey, whom you betrayed. I am Gandalf the White, who has returned from death. You have no colour now, and I cast you from the order and from the Council.' He raised his hand, and spoke slowly in a clear cold voice. 'Saruman, your staff is broken.' There was a crack, and the staff split asunder in Saruman's hand, and the head of it fell down at Gandalf's feet."
Gandalf the White, essentially an incarnate angel, casts no magic spell. He simply states something, and it is true. He speaks efficaciously--his words affect what they signify. In that way, they're sacramental, just like the words "This is my body."
Or "Let there be light."
When God -- directly or through a proxy -- speaks, His works effect exactly what they signify. The words make things happen. Or rather they make things. They are infinitely creative, able to work outside of the normal material order.
Gandalf didn't say "I want your staff to be broken" or "I cast a spell which will break your staff". No, he simply stated that "your staff is broken" and so it was. When Truth speaks, He speaks truth, necessarily. That is power. That is the creative power of God.