The Correct Approach To Fasting (6:16-18).
The idea of fasting in Israel was that of expressing repentance for sin (Nehemiah 9:1-2; Jonah 3:5); or of revealing grief (2 Samuel 1:12; Psalms 35:13; Daniel 10:2). It was an act of self-humbling (Isaiah 58:3), or of going without food for the purpose of engaging in a spiritual exercise, such as prayer, with the aim of greater concentration and a deeper sense of participation (Daniel 9:3; Daniel 10:2-3; Matthew 4:1-2; Acts 13:1-3; Acts 14:23). By turning their thoughts from earthly things they were able to concentrate more on heavenly things, and found that fasting enabled them to concentrate their minds in a spiritual direction. Fasting was intended to foster and inculcate self-humiliation before God, and confession often accompanied it. It was often accompanied by weeping, sackcloth, ashes, dust on the head, and torn clothing (see references above). In Paul's case in Acts 9:9 it probably indicated repentance and a seeking after God. People who felt anguish, or were threatened by impending danger, or felt desperate about some situation, gave up eating temporarily in order to concentrate on presenting some special plea to God in prayer (Judges 20:26; 2 Chronicles 20:3; Ezra 8:21-23; Esther 4:16). Some particularly pious believers fasted regularly (Luke 2:37).
The Pharisees fasted twice a week on Mondays and Thursdays (Luke 18:12), although that was in excess of what was strictly required by the Law, for God had only commanded the people of Israel to fast on one day of the year, the day of Atonement (Leviticus 16:29-31; Leviticus 23:27-32; Numbers 29:7). But during the Exile the Israelites instituted additional regular fasts (Zechariah 7:3-5; Zechariah 8:19), and others were added later. Inevitably there was hypocritical fasting, for it brought to those who participated a reputation for piety. Zechariah appears to speak of those who did it for their own self-satisfaction (Zechariah 7:5). Thus God had to declare that fasting was useless unless it accompanied godly living (Isaiah 58:2-7; Jeremiah 14:12). While fasting was by no means unique to Israel it was something to which others pointed as one of the things that often singled out Jews.
In the early church fasting was probably common (e.g. Acts 13:2) and appears to have been a normal part of Christian self-discipline with Christians later fasting on Wednesdays and Fridays (so The Didache). And this was in line with the fact that while Jesus had not actively encouraged it, He had certainly indicated that He held nothing against it. (Although it is significant that copyists began to introduce the idea into texts where prayer was spoken of in order to justify it, because they were aware of how little justification for fasting the actual text of Scripture gave). Thus it was not fasting that Jesus was speaking against here, but fasting for the wrong motive. Jesus' criticism here was of those who turned their fasting into a public show by making their fasting obvious and drawing attention to themselves, rather than doing it with hearts that were hungry for God. He was not referring to the official fast on the Day of Atonement, (when washing and anointing may well have been abstained from), nor probably to other official fasts.
Analysis of Matthew 6:16-18.
a A “Moreover when you fast, do not be, as the hypocrites, of a sad expression,
b B For they disfigure their faces,
b C That they may be seen of men to fast.
c D Truly I say to you, They have received their reward.
b E But you, when you fast, anoint your head, and wash your face,
b F That you be not seen of men to fast,
a F But of your Father who is in secret,
a G And your Father, who sees in secret, will recompense you.”
Note that in ‘a' they are not to have an obvious sad expression, and in the parallel are to seek to keep their fast secret. In ‘b' they are not to disfigure their faces in order to be seen as fasting, but are to wash their faces and dress their hair so as to hide the fact that they are fasting. Centrally in ‘c' those who do it before men have already received all the reward that they are going to get.