The Hebrew word for "fast" used throughout the Old Testament is tsome. The Greek word used throughout the New Testament is nacetis. Both literally mean "to cover over" or "to affix." The idea is not simply to cover over the mouth--and thus to refrain from eating for a few hours or even a few days--but to affix the attentions to other matters altogether. It is "to focus on" or "to fasten on" spiritual matters rather than merely temporal matters. It is "to hold fast" to Christ--and nothing else. It is to abstain from one thing in order to attain to another.
It is only by a slow and patient walk in grace that we are able to fully comprehend that "man does not live by bread alone" (Matthew 4:4). Fasting is a means that God has appointed to realize anew how it is that Christ has liberated us from the tyranny of the flesh and from the awful surrender of the spirit to the body and its appetite. It is a mighty provocation for us to "humble ourselves under God's mighty hand" (1 Peter 5:6).
Whenever and wherever it is mentioned in the Bible, this gracious appointment of the mature Christian life--the discipline of fasting--has a conspicuously prominent role in humbling God's people so that they can concentrate on spiritual things:
Joshua and the elders kept a solemn fast after their people were defeated by the men of Ai (Joshua 7:6).
Jehoshaphat appointed a day of fasting and prayer throughout his kingdom when the confederated forces of Ammon and Moab came against him (2 Chronicles 20:3).
When Queen Esther felt herself and her people to be in danger from the conspiracy of Haman, she set apart a season of solemn prayer and fasting (Esther 4:16).
Ezra, when setting out on his mission to Jerusalem, assembled the returning captives at the River Ahava, and there proclaimed a fast (Ezra 8:21).
David fasted and prayed in humiliation in the aftermath of the Bathsheba incident (2 Samuel 12:16).
The inhabitants of Nineveh set apart a season of special prayer and fasting following the pronouncement of judgment by Jonah (Jonah 3:7-8).
Even the hardened Ahab fasted and cried for mercy when the judgment of God was denounced against him by Elijah (1 Kings 21:27).
In the New Testament, we see the pious prophetess Anna engaged in serving God day and night with fastings and prayers (Luke 2:37).
Cornelius, the devout centurion, likewise was engaged in fasting and prayer when the Lord first appeared to him (Acts 10:30).
The apostle Paul repeatedly speaks of his habit of waiting on God by fastings as well as by prayer (2 Corinthians 6:5; 11:27).
And even our Lord Jesus entered on His public ministry only after a long season of preparatory fasting (Matthew 4:2).
Mentioned more than seventy-five times in the Bible--more than Baptism, the Lord's Supper, witnessing, or even tithing--fasting is one of the most basic and essential of the disciplines of the Christian life. Of course, iving as we do in these modern times, the very idea of fasting seems a bit arcane and esoteric. Perhaps a tad legalistic. Maybe even bordering on fanatical. But from a Biblical perspective it is just a normal aspect of the Christian faith.