When God purposes a goal He also purposes the means to the goal which is prayer. Prayer is the means that God uses to accomplish His end. Prayer does not change God s purposes, but is His step in the fulfillment of His purpose. So really prayer does not change things, it is the means God includes in His wise plan. Prayer is showing that we are concerned as is God that His will be done.
Persistent prayer takes faith, commitment, and effort.
Paul and Jesus found that their will had to be molded to God s will. It takes little faith, commitment, and effort to pray once about something and then cease. The believer can pray confidently, knowing that our wise and good God will give us, not necessarily what we ask for, but what is best. The Christian sometimes must wrestle with the reality of unanswered prayer. We might even be convinced that something is God s will so that we pray very earnestly.