Both Old and New Testaments talk about fasting, but there is a change in focus from Old to New. Old Testament fasts focused on sorrow or humbling oneself before God. New Testament fasts focus on prayer for spiritual endeavors.
There are two terms for fasting in the Old Testament. Our translations render the first as “fast.” It occurs about 50 times. 1 Samuel 7:6 illustrates the idea of sorrow for sin: “And they fasted that day, and said there, ‘We have sinned against the LORD.'” 1 Samuel 31:13 demonstrates a different kind of sorrow: “Then they took their bones [of Saul and Jonathan] and buried them under the tamarisk tree at Jabesh, and fasted seven days.” Almost all the other Old Testament examples of fasting fall into this category of expressing sorrow.
But there are a few exceptions. According to 2 Samuel 12, David fasted and prayed for the son of Bathsheba. He would have been repenting of his sins of murder and adultery as well, but he himself said when questioned by his servants, “While the child was alive, I fasted and wept; for I said, ‘Who can tell whether the LORD will be gracious to me, that the child may live?’ But now he is dead; why should I fast? Can I bring him back again?” Ezra and the returning captives also fasted and prayed before starting their journey to Jerusalem (Ezra 8:21-23). And Esther wanted the Jews to fast for her before she went in to the king to ask for the lives of her people (Esther 4:16).
The other Hebrew term for fasting is “afflict the soul.” It also was an expression of sorrow. God commanded his people to “afflict their souls” on the tenth day of the seventh month, the Day of Atonement (Lev. 16:29-31, 23:27-32). It was the only required fast. When the Pharisee in the temple boasted that he fasted twice in the week, he was congratulating himself on exceeding the righteousness required by the law. But he missed altogether the meaning of fasting. He was sorry for nothing; he only wanted the praise of men.
Isaiah 58 is an important chapter about Old Testament fasting. It meant nothing to God unless his people were practicing it in connection with righteousness in their own lives and justice and mercy towards their neighbors. “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?” (v. 6).
The New Testament seems to indicate that sorrow should no longer play a part in our fasting. In the synoptic gospels there is a record of some important teaching of Jesus. The disciples of John asked him why his disciples did not fast (Matt. 9:14-17, Mark 2:18-22, Luke 5:33-39). He answered with a question: “Can you make the friends of the bridegroom fast while the bridegroom is with them? But the days will come when the bridegroom will be taken away from them; then they will fast in those days.” In all three accounts of this interchange, Jesus followed his answer immediately with the parables of patching an old garment with new cloth and putting new wine into old wineskins. He was instructing his disciples about the difference between Old and New Testaments. The new wine of the joy of the New Testament cannot be contained in, or properly expressed by, Old Testament forms of worship. The ceremonies of the Old Testament must pass away. No one immediately desires this new wine (Luke 5:39), but it must eventually replace the old. Therefore, new forms of worship (like baptism and the Lord’s Supper) must replace old forms (like the Passover and circumcision).
This is the principle that governed his response to the question about fasting. Fasting as practiced in the Old Testament is not appropriate to the New Testament. The bridegroom is with us now.
However, that does not mean that fasting itself is no longer appropriate. Instead, its focus changes to preparation for spiritual endeavors. All the examples of fasting after the pouring out of the Holy Spirit partake of this character. Some demons can be cast out only by prayer and fasting (Matt. 17:21). As some disciples fasted, the Holy Spirit commanded them to separate Barnabas and Saul for mission work (Acts 13:2). They fasted again and sent them out (v. 3). Paul and Barnabas appointed elders in the churches of Asia Minor, prayed with fasting and commended them to the Lord (Acts 14:23). Husbands and wives are not to deprive each other of sexual intimacy except by mutual consent and for times of prayer and fasting (1 Cor. 7:5).
Prayer is part of fasting. Fasting does not stand by itself as a separate spiritual exercise. We fast so that we may devote ourselves to prayer. I remember talking to a young lady who decided to practice fasting one day when she had to work as a housecleaner. She said that she was so hungry that she could not focus on her work or even do her work effectively. That was a mistake about proper New Testament practice.
Fasting should have a place in the lives of Christians and in the life of the church, but it should always be with a view to spiritual endeavors and in company with prayer.