Prayer implies a relationship between God and man that is not simply a matter of man telling God his needs and God providing for them.  Thus, Baldwin of Canterbury (d. 1190) explains:

"God knows and is known by hearing and in being heard.  Now, he is heard through obedience, so that if he is obeyed, he hears prayers, requests, supplications, vows, and desires.  Man says to God, 'Pay heed to my words with your ears, O Lord' (Psalm 5, 2).  And God says to us, 'Incline your ears to the words of my mouth' (Psalm 77, 1).  For he hears the one who hears him, and does not hear the one who does not hear him.  Thus, it is written, 'The prayer of the man who turns away his ears from hearing the law shall be as an abomination' (Proverbs 28, 9)."