Fasting is a spiritual discipline during which, traditionally, a person abstains from food for a period of time. In practice, the fast may vary in length of time, or in the nature of the abstention. (Some people choose to fast from only certain foods, or from activities or entertainment, etc.)
Jesus fasted, and in fact, seems to assume that his disciples would be fasting on a regular basis. In Matthew chapter 6, Jesus begins his teaching on both prayer and fasting with the word, "when." He says, "When you pray," and "when you fast," and then proceeds to give instructions on how to pray and fast. It seems noteworthy that in neither case does he say, "if you pray," or "if you fast." He assumes that the life of the believer would automatically include both.
Abstaining from food is not the only purpose of a fast. In Isaiah 58, the Lord condemns his people for fasts and other outward manifestations of holiness that were not accompanied by truly righteous living. Isaiah writes,
Behold, in the day of your fast you seek your own pleasure,
and oppress all your workers.
Behold, you fast only to quarrel and to fight
and to hit with a wicked fist.
Fasting like yours this day
will not make your voice to be heard on high.
Is such the fast that I choose,
a day for a person to humble himself?
Is it to bow down his head like a reed,
and to spread sackcloth and ashes under him?
Will you call this a fast,
and a day acceptable to the LORD?
- Moses, Exodus 34
- Nehemiah, chapter 1, chapter 9
- Esther, chapter 4
- Daniel, chapter 9
- Joel, chapter 2
- Jesus, Matthew 4, Matthew 6
- Richard Foster, Celebration of Discipline. Harper Collins, 1988.