Why pray if God knows best? - C.S. Lewis

"Praying for particular things," said I, "always seems to me like advising God how to run the world.  Wouldn't it be wiser to assume that He knows best?""On the same principle," said he, "I suppose you never ask a man next to you to pass the salt, because God knows best whether you ought to have salt or not.  And I suppose you never take an umbrella, because God knows best whether you ought to be wet or dry.""That's quite different," I protested."I don't see why," said he. "The odd thing is that He should let us influence the course of events at all.  But since He lets us do it in one way I don't see why He shouldn't let us do it in the other."