We can do no thing of real power until we have done the prayer thing. Here is a man by my side. I can talk to him. I can bring my personality to bear upon him, that I may win him. But before I can influence his will a jot for God, I must first have won the victory in the secret place. Intercession is winning the victory over the chief, and service is taking the field after the chief is driven off. Such service is limited by the limitation of personality in one place. . . . Prayer puts man into direct dynamic touch with a planet.
S. D. Gordon. From the Desiring God blog.