Here's why John Piper wrote the book "Fasting"
My goal and my prayer is that this book awakens our hunger. Our hunger to put God back at the heart of all things, for the joy of all peoples. Fasting demonstrates the reality of this hunger and rekindles its flame. It intensifies spiritual desire. He is our steadfast ally against what makes us dependent on innocent pleasures. It is to our physical life what the exclamation mark is at the end of this sentence: "See how much I thirst for you, O God, and how I can't wait for your glory to be spread throughout the world. whole ! "
We might imagine that those who most often revel in the feast of fellowship with God would be the least hungry for God. They regularly turn away from the innocent pleasures of the world and linger for a long time in the presence of God, immersing themselves in the revelation of his Word. There, through meditation and faith, they eat the Bread of Heaven and drink the Living Water. Well, paradoxically, these people are not the least hungry among the saints ... rather the reverse is true. The strongest and most mature Christians I have encountered are also the most hungry for God. Logic would dictate that those who eat the most are the least hungry. But that's not how things work when the fountain is endless, the feast endless, and the Lord so glorious!
When you stand firm in the work done by God in Christ, and begin to drink from the river of the water of life, to feed on the Bread of heaven, when you know that all your aspirations are finally satisfied… you only become more hungry for God. And the more you experience the satisfaction that comes from God in this world, the more you yearn for the world to come. As C. S. Lewis said, "Our desires are the most precious of our possessions."
The closer you walk with Christ, the more you hunger for Christ… the more you desire to go to heaven… the more you yearn to know “all the fullness of God”… the more you want to be done with sin… the more you desire the Bridegroom to return… the more you desire the Church to be renewed and purified by the beauty of Jesus… the more you desire a great revival in the big cities… the more you desire to see the light of the Gospel of glory of Christ to penetrate the darkness of all unreached peoples of the world… the more you desire that the false representations of the world capitulate before the force of Truth… the more you desire that suffering be relieved, tears dried and death destroyed… more you long for all evil to be turned into good, and for the righteousness and grace of God to fill the earth, as water fills the sea.
If you do not feel an intense desire within you to see the glory of God spread, it is not because you have had a long drink and your thirst has been quenched. No. It's because you've nibbled too long at the world's table. Your soul is filled with small things, and there is no more room for all that is great. God did not create you for this purpose. To be hungry for God is possible. And you can experience it. I invite you to turn away from the numbing effects of food and the dangers of idolatry. Say, through a simple fast:
"See how much I long for you, O God! "