Of the three disciplines in Matthew 6:1-18, fasting is the most difficult because evangelical Christians have been hesitant to participate in fasts. For most, they would prefer a good potluck to a fast!
However, fasting was common in the ancient world and is still an important spiritual discipline for many religious people. The practice of fasting is considered a critically important method for getting in touch with spiritual things. For example, Bonhoeffer said “Satiated flesh is unwilling to pray and unfit for self-sacrificing service” (Bonhoeffer, Discipleship, 158). McKnight considers this an example of the instrumental view of fasting: one fasts in order to gain some spiritual benefit. But he also states clearly this view of fasting is simply not found in the Bible (McKnight, Sermon, 193).
Jesus does not command almsgiving, prayer or fasting. He simply assumes his disciples will do these basic spiritual disciplines. What he commands is a re-thinking of the how these commonly practiced spiritual acts of worship should be done. In all three cases he turns the focus away from the one doing the act and toward God.
What did it mean to fast at the time of Jesus?
In the Old Testament, fasting was required only on the Day of Atonement (Lev 16:29-31, 23:26-32), Acts 27:9 simply calls the Day of Atonement “the Fast.” But there are other examples of fasting in the Old Testament in response to either an important or terrible event. The death of a loved one is often associated with “sackcloth and ashes,” perhaps fasting as well. In 1 Samuel 31:13 the people of Jabesh Gilead mourn the death of Saul by fasting for seven days. In 2 Sam 1:12, David and his men fasted and mourned Saul and Jonathan (although this fast only lasted until the evening). In Judges 20:26 the people fasted before the Lord all day before a battle the following day. In 1 Sam 7:6 Saul commanded a fast until a battle was won (although this is considered a rash vow). The people responded with fasting in response to the judgment of God in the exile (crises Isa 58:3-5; Jer 14:12; Zech 7:5). This is similar to the fasts in Esther 4:16 and Ezra 8:23. Psalm 35:11-16 is an example of responding to oppression. David has been attacked by “malicious witnesses” and his response is sackcloth and ashes (cf., Psalm 69:10-11). For Second Temple period Jews, fasting had been encumbered by additional regulations.
There are a few examples of fasting in the New Testament which is not associated with mourning. In Luke 2:37 Anna is described as fasting and praying in the Temple. Paul and Barnabas are appointed to a mission after prayer and fasting (Acts 13:2-3) and Paul and Barnabas appointed elders only after a time of prayer and fasting (Acts 14:23). Paul refers to fasting in 2 Corinthian 6:5 and 11:27 although he may mean a time of hunger since it is in a list of suffering he has experienced.
Luke 5:33 states John the Baptists and his disciples “fasted often,” as do the Pharisees (Mark 2:18/Matt 9:14). In contrast, the disciples of Jesus did not fast in the same way.
The Pharisees fasted twice a week (Luke 18:12), on Thursday and Monday. According to tradition, Moses ascended Mount Sinai on Thursday and descended on Monday. Those two days were the “market” days, when Jerusalem was the busiest, and fasting would have the largest audience. The early Christian church manual Didache 8 says “But do not let your fasts coincide with those of the hypocrites. They fast on Monday and Thursday, so you must fast on Wednesday and Friday.”
Fasting was important in the early church and is mentioned thirty times in the New Testament and it is never condemned. As in the Old Testament, fasting marked times of sorrow or prayer, often accompanying a decision. Keeping the Old Testament texts cited above in mind, a person might fast during the day and have a small meal in the evening.
Polycarp, To The Philippians 7.2 Therefore let us leave behind the worthless speculation of the crowd and their false teachings, and let us return to the word delivered to us from the beginning; let us be self-controlled with respect to prayer and persevere in fasting, earnestly asking the all-seeing God “to lead us not into temptation,” because, as the Lord said, “the spirit is indeed willing, but the flesh is weak.”
Bibliography: N. K. Gupta, “Fasting,” page 270 in Dictionary of Jesus and the Gospels (Second Edition).