He places them on our lips for how and what we should pray, so that we may see how heartily He pities us in our distress, and we may never doubt that such prayer is pleasing to Him and shall certainly be answered.
Luther's Large Cathecism III.22
Besides this, we should be moved and drawn to prayer. For in addition to this commandment and promise, God expects us and He Himself arranges the words and form of prayer for us.