16 “And when you fast, do not look gloomy like the hypocrites, for they disfigure their faces that their fasting may be seen by others. Truly, I say to you, they have received their reward. 17 But when you fast, anoint your head and wash your face, 18 that your fasting may not be seen by others but by your Father who is in secret. And your Father who sees in secret will reward you. 
The first two examples of Christian piety that Jesus gives in the middle of the sermon on the mount are not particularly difficult to understand. For most people, prayer and charity make sense and are familiar even to those who don’t quite understand them completely or practice them. But Christ’s third example of piety, fasting, is somewhat strange in our modern Westernized world. Abstaining from food for some spiritual end seems unnecessary to most people. To others it may even seem foolish or absurd.
You may recall that this is the third statement Jesus has made so far in this sermon about public displays of piety that ought to be between the follower and God. In 6:2-4, he said:
2 Thus, when you give to the needy, sound no trumpet before you, as the hypocrites do in the synagogues and in the streets, that they may be praised by others. Truly, I say to you, they have received their reward. 3 But when you give to the needy, do not let your left hand know what your right hand is doing, 4 so that your giving may be in secret. And your Father who sees in secret will reward you. 
In 6:5-6, he instructed:
5 And when you pray, you must not be like the hypocrites. For they love to stand and pray in the synagogues and at the street corners, that they may be seen by others. Truly, I say to you, they have received their reward. 6 But when you pray, go into your room and shut the door and pray to your Father who is in secret. And your Father who sees in secret will reward you. 
As with charitable giving and prayer, Jesus assumes his disciples will fast. The issue is not whether to do it but how. In a culture where few now give serious attention to fasting as a religious discipline (as opposed to token acts like giving up chocolates during Lent) this assumption is surprising to most believers.
HEALTH AND FINANCES
One easy, but superficial, way to understand fasting is to realize that some Christians fast for financial reasons. They might forego lunch once or twice a week in order to preserve the money they would have spent to contribute toward their church or a mission work.
Fasting and intermittent fasting are becoming more popular with the general public for improving health and fighting the battle of the bulging waistline. Personally, I have found it to be highly beneficial in managing both my waistline and my blood sugar. But such fasting, at least for me, is not an act of spiritual devotion as it is an act of self-preservation.
Fasting to improve one’s financial situation or one’s health may make sense. But unfortunately, those situations are not a great deal of help to us in tackling this passage. In fact, when we read scriptures that mention fasting, financial reasons or health reasons are not really under consideration. You might even be surprised to learn that fasting under the old covenant and under the new covenant are done for different purposes.
OLD COVENANT FASTING
In the Old Testament, fasting had an entirely different purpose from that in the new. Moreover, the central text upon which this change takes place is the text we are studying this morning in Matthew chapter 6.
What was the purpose of fasting under the old covenant? Fasting was always connected with mourning for sin and repentance. The entire Hebrew nation was to fast on the Day of Atonement, for this was the day they were to mourn for their sin and look for the reconciliation which God provided through sacrifices. This was the only occasion in the Old Testament on which Israel was specifically commanded to fast.
From that one command, the practice spread to occasions of national disaster or national repentance. The prophet Joel (2:12) issued God’s call for fasting to repentance. Nineveh repented with fasting after hearing Jonah’s preaching (Jonah 3:5). Israel fasted following the civil war with the tribe of Benjamin (Judges 20:26). The nation fasted over the death of Saul and Jonathan (1 Samuel 31:13). They fasted as part of a national revival under the ministry of the prophet Samuel (1 Samuel 7:6). The Hebrew word for fasting carries the flavor of the repentant humbling of the soul before God.
The proof that OT fasting was for repentance is found in two other texts where it is mentioned. The first is Matthew 9:14–15, where Jesus is speaking to the disciples of John the Baptist, who practiced fasting. These disciples came to Jesus to ask why his disciples did not fast. Jesus answered, “How can the guests of the bridegroom mourn while he is with them?” In other words, the disciples did not fast because fasting implied sorrow, and the years of Jesus’ earthly ministry were joyous.
The most extensive discussion of fasting in the Old Testament occurs in Isaiah 58:1–7. Here the people of Israel reminded God that they had fasted but complained that fasting had not produced the results they were seeking. God answered by saying, “Your fasting ends in quarreling and strife, and in striking each other with wicked fists.… Is not this the kind of fasting I have chosen: to loose the chains of injustice and untie the cords of the yoke, to set the oppressed free and break every yoke? Is it not to share your food with the hungry and to provide the poor wanderer with shelter—when you see the naked, to clothe him, and not to turn away from your own flesh and blood?” In other words, God says that mere ceremonial fasting means nothing. The only fasting that was of any value was that which involved repentance of sin resulting in a transformed and charitable life. This is what fasting implied before Christ’s coming.
NEW COVENANT FASTING
After Jesus came, fasting was thought of differently. Early Christians knew that their sin had been forgiven and did not need to mourn for it in the way men did before Christ’s death, resurrection, and glorious ascension. They did not fast for their sin. They did not fast in sorrow. But they did fast. They wanted to set aside the normal distractions of this life in order to seek God’s clear direction for their lives. Fasting became a discipline by which they waited upon God while asking him to reveal his will.
The apostle Paul linked the concept of fasting to the idea of “watching.” In 2 Corinthians 6:4-5 [NSB] he wrote that apostles conduct themselves:
as the ministers of God, in much patience, in afflictions, in necessities, in distresses, in stripes, in imprisonments, in tumults, in labors, in watchings, in fastings…. 
Paul is saying that fasting is a spiritual exercise by which he waited upon God to reveal his will to Paul.
At this point we might ask the question, “Is there any evidence that God actually responded to such fasting by revealing his will?” Is this theoretical purpose borne out in practice? The answer is yes. Even more, the instances themselves show that fasting was linked to two of the most significant advances of the gospel in the ancient world following Pentecost.
The first event was the opening of the gospel to the gentiles through Cornelius by the ministry of Peter. In the 10th chapter of Acts, after Peter had received his vision of the great sheet of ceremonially unclean food let down from heaven and had gone because of that vision to the home of the gentile centurion, Cornelius spoke to explain the reason he had called Peter, saying:
Four days ago, about this hour, I was praying in my house at the ninth hour, and behold, a man stood before me in bright clothing 31 and said, ‘Cornelius, your prayer has been heard and your alms have been remembered before God. 32 Send therefore to Joppa and ask for Simon who is called Peter. He is lodging in the house of Simon, a tanner, by the sea.’ 33 So I sent for you at once, and you have been kind enough to come. Now therefore we are all here in the presence of God to hear all that you have been commanded by the Lord. 
The language of the text and the practice of the early believers strongly suggest that Cornelius was fasting as he prayed and received his vision.
Another example is found in Acts 13:1-3, recounting the start of Paul’s missionary journeys:
Now there were in the church at Antioch prophets and teachers, Barnabas, Simeon who was called Niger, Lucius of Cyrene, Manaen a lifelong friend of Herod the tetrarch, and Saul. 2 While they were worshiping the Lord and fasting, the Holy Spirit said, “Set apart for me Barnabas and Saul for the work to which I have called them.” 3 Then after fasting and praying they laid their hands on them and sent them off. 
Yet another example is found in Acts 14:21-23:
21 When [Paul and Barnabas] had preached the gospel to that city and had made many disciples, they returned to Lystra and to Iconium and to Antioch, 22 strengthening the souls of the disciples, encouraging them to continue in the faith, and saying that through many tribulations we must enter the kingdom of God. 23 And when they had appointed elders for them in every church, with prayer and fasting they committed them to the Lord in whom they had believed. 
Something important to note in these passages is that fasting is not a practice that changes God’s will, it is a practice that changes us as we submit to God and seek his specific direction in our lives. It is not some sacrifice we make for God to get something from him. God cannot be manipulated.
We see in these passages from Acts that there is a change in the use and purpose of fasting traced to the very words of Jesus that we are studying this morning. He thought that it was to be a personal exercise between the soul of the individual and God.
Jesus promised, “your Father who sees in secret will reward you.” They’re reward is not money, health, a promotion at the office, or any of our other idolatrous wishes we want fulfilled. It is the reward of the Father’s presence and the revelation of his will. Fasting is valuable to that end alone so long as we do it before the Lord and not men.
In the NT as a whole there is little explicit instruction on fasting; it is simply mentioned occasionally (and never in the epistles) as something Christians sometimes did. Jesus himself fasted … in the wilderness (4:2), but there is no other record of his doing so subsequently, and indeed it was the lack of fasting by him and his associates which was commented on in Matthew 9:14, though in his reply, Jesus does assume his disciples would be fasting at a future date (9:15).
In Acts we are told of prayer and fasting on two occasions as an accompaniment to important decisions (Acts 13:2–3; 14:23), but not of any regular pattern of fasting. When Paul speaks of “fasting” as part of his apostolic sufferings (2 Cor 6:5; 11:27) the reference is to more likely to an involuntary shortage of food rather than to deliberate abstention.
It is not until Didache 8:1 that we find instruction on regular fasting for Christians—twice a week, like the Pharisee in Luke 18:12. In view of the scarcity of evidence, it is hard to decide whether the fasting Jesus here assumes is expected to be a regular practice (as in the Didache) or only on special occasions as in Acts. He simply comments on the familiar Jewish practice with the expectation his disciples will fast.
The sort of fasting envisaged here is presumably that of choice rather than of routine since there would be little point in putting on a show to impress people with one’s fasting if it were already known and expected. In Matthew 9:14–17 we find the voluntary fasting of the Pharisees used as a stick with which to beat the Jesus movement, which is alleged not to take its religious obligations sufficiently seriously.
The argument of course assumes that other people knew the Pharisees were fasting. Just how the “hypocrites” made their fasting visible (by making their faces “invisible”!) is not clear, but there is a delicious irony in Jesus’ play on words between aphanizō (“hide”) and phainomai (“everyone can see;” cf. also v. 18). Their “miserable” look was felt by some, then as now, to be a suitable expression of religious devotion.
By contrast, Jesus’ disciples’ washing and anointing are part of the everyday bodily care which were sometimes forgone as part of the self-affliction involved in fasting. Anointing, like the washing of the face, represents normal cosmetics (Luke 7:46; cf. Ruth 3:3; 2 Sam 14:2; 2 Chr 28:15; Dan 10:3), not an artificial show of happiness; everything is to be outwardly normal. Fasting, like alms-giving and prayer, is to be between the disciple and God. No-one else should know. Perhaps that is why we know so little of early Christian practice in this regard!
Fasting is not an external religious exercise. It is a period of abstinence in which the believer can seek God’s will. That being said, it is also true that the essence of fasting can be achieved in other ways. It can be achieved by abstaining from things. That can be more important than simply not eating.
Fasting means voluntary abstinence for a time from various necessities of life such as food, drink, sleep, rest, entertainment, and the like. It does not view the necessities of life as unclean or unholy. Fasting implies that our souls at certain times need to concentrate more strongly on the one thing most needful – our relationship with our Dear Heavenly Father. In fasting, we temporarily renounce certain things which in themselves, are permissible and profitable.
One thing for which we should set aside our normal routine is spending time in scripture, individually and with other believers. That is really the ultimate point. For it is in Bible study more than in other disciplines that God speaks to us and where he reveals his way and his will to us. Early believers had the Old Testament scriptures. But only the very wealthy could afford a personal copy of even one book of scripture. They had no New Testament. For them, fasting and praying was seeking after the extraordinary acts of God like visions and prophecies.
For us, reading scripture is the ordinary means by which God communicates with us in a time when all scripture has been written and canonized. It is in Bible study and meditation and prayer more than any other ways that God speaks to us and reveals his will to us.
Sometimes our fasting will lead us away from entertainment, like watching television. I can fast from my entertainment because I am seeking the will of God in scripture and in meditation and in prayer. Paul and Barnabas fasted together when considering the appointment of elders in the local churches. So, fasting is not always done by one person in secret. There are certain times and circumstances when our elders agree to fast and pray over a matter.
God is the one who calls us to fast. It’s not something we do for God. It is something he does in us and for us. The Holy Spirit drove Jesus into the wilderness to fast. Jesus did not come up with the idea on his own as a way to get something from God. The Holy Spirit moved Paul and Barnabas to fast.
How all of this information applies to you it’s up to you to determine. After all, fasting is a private event between you and God. Don’t feel guilty if you have not been called to fast. Whatever your daily routine or habits, there are undoubtedly some things that you may want to lay aside temporarily to spend time with God. After all, you have this promise from Jesus, “And your Father who sees in secret will reward you.”
 The Holy Bible: English Standard Version (Wheaton, IL: Crossway Bibles, 2016), Mt 6:16–18.
 The Holy Bible: English Standard Version (Wheaton, IL: Crossway Bibles, 2016), Mt 6:2–4.
 The Holy Bible: English Standard Version (Wheaton, IL: Crossway Bibles, 2016), Mt 6:5–6.
 France, 253.
 Boice, 209.
 Id., 209–210.
 The Holy Bible: English Standard Version (Wheaton, IL: Crossway Bibles, 2016), Ac 10:30–33.
 The Holy Bible: English Standard Version (Wheaton, IL: Crossway Bibles, 2016), Ac 13:1–3.
 The Holy Bible: English Standard Version (Wheaton, IL: Crossway Bibles, 2016), Ac 14:21–23.
 France, 254.
 France, 255.