The hardest part about writing the Prove It books is finding good quotes. Here's an excellent one from C.S. Lewis on petitionary and intercessory prayer:

We have long since agreed that if our prayers are granted at all they are granted from the foundation of the world. God and His acts are not in time. Intercourse between God and man occurs at particular moments for the man, but not for God. If there is—as the very concept of prayer presupposes—an adaptation between the free actions of men in prayer and the course of events, this adaptation is from the beginning inherent in the great single creative act. Our prayers are heard –don’t say “have been heard” or you are putting god into time—not only before we make them but before we are made ourselves.
Letters to Malcolm: Chiefly on Prayer.