Our appetites dictate the direction of our lives--whether it be the cravings of our stomachs, the passionate desire for possessions or power, or the longings of our spirits for God. But for the Christian, the hunger for anything besides God can be an archenemy, while our hunger for God--and him alone--is the only thing that will bring victory.
Do you have that hunger for Him? As John Piper puts it: "If we don't feel strong desires for the manifestation of the glory of God, it is not because you have drunk deeply and are satisfied. It is because we have nibbled so long at the table of the world. Our soul is stuffed with small things, and there is no room for the great." If we are full of what the world offers, then perhaps a fast might express, or even increase, our soul's appetite for God.
Between the dangers of self-denial and self-indulgence is this path of pleasant pain called fasting. It is the path John Piper invites you to travel in this book. For when God is the supreme hunger of your heart, He will be supreme in everything. And when you are most satisfied in Him, He will be most glorified in you.