Why Pray if God is Sovereign? (Romans 8:26 (LD 45)

The Lord is a God who rules over all things.  He is king over the heaven and the earth.  He is the one who orders and controls our destiny.  So, if this is all true then why pray?  It is not like you are going to change the mind of a God whose mind does not change.  It is not like you are going to inform Him of something that He does not already know.  So, why is prayer so necessary and significant for the Christian life?