Pascal says that God 'instituted prayer in order to allow His creatures the dignity of causality'. It would perhaps be truer to say that He invented both prayer and physical action for that purpose. He gave us small creatures the dignity of being able to contribute to the course of events in two different ways. He made the matter of the universe such that we can (in those limits) do things to it; that is why we can wash our own hands and feed or murder our fellow creatures. Similarly, He made His own plan or plot of history such that it admits a certain amount of free play and can be modified in response to our prayers. If it is foolish and impudent to ask for victory in a war (on the ground that God might be expected to know best), it would be equally foolish and impudent to put on a mackintosh - does not God know best whether you ought to be wet or dry?
C.S. Lewis, “Work and Prayer,” God in the Dock (Eerdmans: 1970) 106.