“Man shall not live by bread alone, but by every word that comes from the mouth of God” (Matthew 4:4). With these words, Jesus rebuked Satan who had come to tempt Him in the midst of His fasting. Few words could describe more clearly the purpose of this neglected part of Biblical piety. Fasting is, therefore, an expression of dependence upon God and a striving after those things which will never pass away. “’Food is meant for the stomach and the stomach for food’—and God will destroy both one and the other” (1 Corinthians 6:13). “But seek first the kingdom of God and his righteousness, and all these things will be added to you” (Matthew 6:33).
That fasting is a neglected practice is a real problem, because Jesus commands it in no less uncertain terms than prayer: “And when you fast” (Matthew 6:16), not “if you fast.” Jesus condemns the misuse of fasting, turning it into a public spectacle as a means of attracting approval rather than focusing on the things of God. Fasting therefore most often belongs to the category of secret piety: “But when you fast, anoint your head and wash your face, that your fasting may not be seen by others but by your Father who is in secret. And your Father who sees in secret will reward you” (Matthew 6:17-18).
Fasting, like any other part of Biblical piety, is easily abused. King Darius fasted out of anxiety (Daniel 6:18). Fasting can be merely external, bowing the head and spreading sackcloth and ashes (Isaiah 58:5). Men may boast of their fasting as if it meant something before God (Luke 18:11-12). But “in the day of your fast, you seek your own pleasure” if that is the case (Isaiah 58:3). The acceptable fast of the Lord builds up and does not puff up. It advances holiness and piety and does not seek its own glory.
Fasting and prayer go together, because fasting is not an end in itself. Fasting for the sake of fasting makes it merely external. But the reasons for fasting in the Bible are many. Very frequently, fasting is a sign of repentance, an intense form of sorrow over sin (Judges 20:26; 1 Samuel 7:6; 1 Kings 21:27-29; Ezra 9:5; Nehemiah 9:1-2; Jeremiah 36:6-9; Daniel 9:3; Joel 2:12-16; Jonah 3:5). Men may fast also as a part of mourning over death (1 Samuel 31:13; 2 Samuel 1:12; 1 Chronicles 10:12) or at distressing news (Nehemiah 1:4; Esther 4:3-16; Daniel 10:2-3). Fasting may also be a part of intercession, imploring God’s mercy (2 Samuel 12:16-23). In such cases, the motivation for fasting is humility before God, especially since we are deserving of His wrath. “Naked I came from my mother’s womb, and naked shall I return. The Lord gave, and the Lord has taken away; blessed be the name of the Lord” (Job 1:21).
But fasting may also be undertaken for “positive” reasons. Ezra fasts and prays as a part of asking for God’s protection on the journey to Jerusalem (Ezra 8:21-23). It therefore emphasizes that coming and going, as with all things, are in the Lord’s hands. Anna fasts as a part of worship (Luke 2:37). Fasting is therefore not an extraordinary practice. Finally, fasting precedes important decisions within the Church (Acts 13:2-3; 14:23). God’s will should be sought in all things, and fasting emphasizes this need for the guidance of the Holy Spirit. It should also be noted that fasting is not always a part of secret piety, since the kings sometimes called upon all people to fast together (2 Chronicles 20:3). While fasting is most often individual, the whole body of Christ may fast together as a part of public prayer.
Biblically speaking, fasting is a total restraint from eating and drinking. Abstaining from things other than food is not, strictly speaking, fasting. Paul, for example, commends a temporary abstention from sex within the bounds of marriage for the purpose of prayer, but this is not fasting (1 Corinthians 7:5). This sort of abstaining may be necessary as a form of self-control, but fasting in the Bible does not seem to be divided into degrees. “Partial fasts,” or refraining only from a certain type of food or drink, seems to be more akin to abstaining. Too often, “giving up” something, especially in the liturgical season of Lent, is done because it is “bad for me anyway.” While sweets may indeed be an idol, Biblical fasting is not a matter of health (Psalm 109:24-25). Christ did not stop eating only donuts while wandering forty days in the wilderness.
As for when one should fast, this is a matter of Christian liberty. There is a benefit to regularly scheduling a fast, such as on a particular day, provided it does not become an occasion for stumbling. Allowing fasting to happen “whenever,” like prayer, will probably mean never doing it at all. One must make allowances for those who are unable to fast for a variety of reasons (such as health problems or the young), but inconvenience is not a reason to avoid doing it. The length of fasting is also a matter of liberty, though extremely short duration are more prone to abuse. Fasts of supernatural lengths are obviously not a goal, but they should be as long as needed for whatever reason they are undertaken.
But above all, fasting and prayer go together. When you fast, pray to your Father who sees in secret. Fasting does not intensify prayer, as if God will really listen to the one who prays and fasts. That is Gentile thinking. Rather, fasting reminds us of the one thing needed, so that we may be able to say with our Lord Jesus Christ: “My food is to do the will of him who sent me and to accomplish his work” (John 4:34).