In this section of the Sermon on the Mount, Christ is continuing His general point that genuine Christian living is to be before the Father, and not primarily before men. The point He makes about fasting is the same point he has already made about giving and prayer.
"Moreover, when you fast, do not be like the hypocrites, with a sad countenance. For they disfigure their faces that they may appear to men to be fasting. Assuredly, I say to you, they have their reward. But you, when you fast, anoint your head and wash your face, so that you do not appear to men to be fasting, but to your Father who is in the secret place; and your Father who sees in secret will reward you openly" (Matt. 6: 16-17).
First, we should note something about an odd background assumption. Notice that when the hypocrites want to draw attention to their piety, they do so by means of a sad countenance. But true piety is determined by the Word of God, and not by our assumptions of appropriate emotions. Piety is not measured by a long face, but rather in gladness and joy.
What is fasting? Fasting is the practice of abstaining from food for a period of time in order to humble oneself before God. "Then I proclaimed a fast there at the river of Ahava, that we might humble ourselves before our God, to seek from Him the right way for us and our little ones and all our possessions" (Ezra 8:21).
This need to humble ourselves may come from various quarters. We may feel ourselves in danger (2 Chron. 20:3), be overwhelmed by the providential judgments of God (Joel 1:14), or simply because we have a petition we want to place before the Lord (Est. 4:16).
At the same time, fasting is not the way to operate the celestial vending machine. We cannot say the magic words, or do the magic thing, that will somehow put the sovereign God into our debt. Consider the teaching of Isaiah 58:
In that passage, the hypocrites have a question. ‘Why have we fasted,’ they say, ‘and You have not seen? Why have we afflicted our souls, and You take no notice?’ "In fact, in the day of your fast you find pleasure, and exploit all your laborers (Is. 58:3). Isaiah confronts the same kind of externalism which Christ condemns in the Sermon on the Mount.
But it is also important to note that God does not demand a mystical pietistic internalism to counter this problem. Consider verse 6. God says, "Is this not the fast that I have chosen: To loose the bonds of wickedness, to undo the heavy burdens, to let the oppressed go free, and that you break every yoke?" (Is. 58:6).
So as we fast, what must accompany, and completely overshadow, any biblical refraining from food?
1. We must share with hungry, poor, and naked (v. 7);
2. We must see the manifestation of healing and righteousness (v. 8);
3. We must see the glory of the Lord as our bodyguard (v. 8);
4. We must see the Lord pleased to answer our prayers (v. 9);
5. We must have nothing to do with the wicked pointing of fingers. "You . . .!" (v. 9);
6. We must extend ourselves to the afflicted (v. 10);
7. We must be recipients of the grace of God (11-12);
8. We must delight in the Lord's Day (v. 13);
9. We must delight in the Lord (v. 14).
If any of these things is missing or twisted, a man may be proficient in imitating the Pharisees in how they fasted. But he is not fasting. He is just going hungry, and he already has his empty reward.