The Pontifications blog quotes Cardinal Christoph Schoenborn of Vienna quoting Blaise Pascal on why God gave us prayer. After all, God does not need our prayers before He will act. He knows our needs before we can even voice them.
Blaise Pascal asked: “Why did God institute prayer? To give his creatures the dignity of causality.” Saint Thomas explains this in his long quaestio on prayer.
There are things that we can do because it is in our power to do them. There are things that, although not in our power to do, can still be done by us when we ask that they be done by someone who can do them. Petitionary prayer, therefore, is for Thomas the primary form of prayer. It shows that we are in need, that we depend upon God. It is also the recognition that God really can achieve what we can only request. That is why petitionary prayer always has an element of adoration, of praise and thanksgiving.
I like that. I will have to meditate on that later.