In John Frame’s Systematic Theology, he gives 3 reasons why we pray.
- Divine Command (God commands us to pray)
- Fellowship with God (through prayer we experience a closeness to God)
- Prayer changes things.
Concerning the last point, here’s a couple helpful quotes:
“God ordains prayer as a means to change history. There are things that happen because of prayer, and things that do not happen because of no prayer.”
“Now, of course, prayer doesn’t change the eternal plan of God. But within that eternal plan are many plans for means and ends. God ordains that crops will grow, but not without water and sun. He ordains that people will be saved, but (ordinarily) not without the teaching of the Word. And he ordains that we will have everything we truly need, but not without prayer. God’s eternal plan has determined that many things will be achieved by prayer, and many things will not be achieved without prayer.”