Lewis on Prayer
Here's C. S. Lewis, in God in the Dock:
Prayers are not always ... “granted”. This is not because prayer is a weaker kind of causality, but because it is a stronger kind. When it “works” at all it works unlimited by space and time. That is why God has retained a discretionary power of granting or refusing it. Except on that condition prayer would destroy us. It is not unreasonable for a headmaster to say, “Such and such things you may do according to the fixed rules of the school. But such and such other things are too dangerous to be left to general rules. If you want to do them you must come and make a request and talk over the whole matter with me in my study. And then - we’ll see.”