(excerpt from John Piper, Revival and Prayer, June 6, 1986)
And when you fast, do not look dismal, like the hypocrites, for they disfigure their faces that their fasting may be seen by men. Truly, I say to you, they have their reward. But when you fast, anoint your head and wash your face, that your fasting may not be seen by men but by your Father who is in secret; and your Father who sees in secret will reward you. (Matthew 6:16-18)
The point here is that fasting is a feast.
It is not a giving up of food for its own sake.
It is a giving up of food either for the praise of men or for the reward of the heavenly Father. We are always driven to fast because we hunger for something more than food.
That is the meaning of fasting: it cries out, “This I want more than the pleasure of food!”And “this” can be the admiration that men give to people with will power, or it can be the reward we seek from God alone without regard to the praise of men.
Jesus, of course, says, “Feast on God not man! Desire God in secret, not the praise of men in public.” This is just another way of saying what William Sprague said about seriousness. No one engages in secret fasting in the presence of God alone with a spirit of levity or trifling. Even when you wash your face so as not to look dismal, there will be strong, earnest, serious longings in the soul.
Secret fasting makes you real with God. It is just for God and it tests the authenticity of your hunger for his Spirit.
Well, it is time for lunch, and I need to find a way to invite you to stay for part two and for prayer without making those of you who have to go feel like second-class Christians. Here’s how I can do it. We will just assume that you had an unbreakable appointment or that you are going away to fast in secret.
Revival and Fasting Bethlehem Day of Prayer – Desiring God