Open Matthew 6:16-18.
There’s a fascinating background to Jesus’ teaching on fasting. After all, Judaism was primarily a religion of feasting.
Christians tend to think of the sacrifices in the Old Testament as animals being slaughtered to forgive people’s sins. Sacrifices were about maintaining the covenant, but they were mostly about eating at God’s table. Every morning and evening, priests offered animals to God and ate the fellowship meal with him on behalf of the people. Three times a year, the people were called to join in the “feasts” (Exodus 23:14-16; 34:18-25). They didn’t come empty handed. They brought their animals, and ate the feast with God. The feasts reflected the meal provided by the heavenly sovereign to Israel’s leaders at Sinai in celebration of the covenant (Exodus 24:11).
In addition to this regular feasting, they fasted in times of special need (e.g. 1 Samuel 7:6; 31:13; 2 Samuel 12:16-23; Psalm 35:13). Then came the great tragedy of 586 BC. When the temple was destroyed, there was no more place of sacrifice. The feasts stopped. For the first time, they had regular fasts in place of feasts. 70 years later, a second temple was dedicated, so the feasts could resume. The people of Bethel weren’t sure what to do at this point. Should they continue their regular fasts or not? Zechariah responded by questioning their motives in fasting or feasting:
Zechariah 7:5–6 (ESV)
5 Say to all the people of the land and the priests, “When you fasted and mourned in the fifth month and in the seventh, for these seventy years, was it for me that you fasted? 6 And when you eat and when you drink, do you not eat for yourselves and drink for yourselves?”
If they fasted for the right reason — because YHWH was absent from the table for those 70 years — now that he had returned the fasts should once again become feasts:
Zechariah 8:3, 19 (ESV)
3 Thus says the Lord: I have returned to Zion and will dwell in the midst of Jerusalem …
19 The fast of the fourth month and the fast of the fifth and the fast of the seventh and the fast of the tenth shall be to the house of Judah seasons of joy and gladness and cheerful feasts.
In Jesus’ time, regular fasting continued. A religious person might boast of fasting two days a week (Luke 18:12). They are not fasting for the temple which had been rebuilt. What had not been restored was the kingship. This seems to be a point of difference between Jesus and others. The Pharisees were fasting. John the Baptist’s disciples were fasting. Jesus’ disciples were not. If the kingship was re-established, presumably the fasting would turn to feasting. If the bridegroom were already present, the guests should celebrate, not mourn. Jesus’ disciples did not fast because the king was already present among them (Matthew 9:14-15).
That’s the message Jesus delivers later to John’s disciples, but right now (in the Sermon on the Mount) he asks a more basic question: for whom are you fasting? For God, or for people?
When fasting day arrives, the “actors” leave their hair uncombed and attire themselves in a dishevelled manner so as to remind everyone in town of their civic duty to comply with their decrees and fast that day. In other words, the reason they present themselves as fasting is that it suits their power-claim to be the ones whom everyone must follow. Don’t do it, Jesus says. Don’t follow them. It’s all a farce, a mock-up, fake leadership. They will never give you the kingdom. They’re acting for people, and that’s all the reward they will get.
If you want to fast, don’t do it for people. Do it for God, in a way that others can’t see. When your Father sees you asking for his kingship, he will reward you with the thing you’re seeking: his kingship.
Matthew 6:17-18
17 When you (all) fast, don’t become dejected like the actors do. They present dishevelled faces so people will notice them fasting. I tell you the truth: that’s all the reward they’ll get.
18 When you (individually) fast, shower and freshen up, so your fasting isn’t displayed to people but privately to your Father. Your Father — the one who sees in private — will reward you.
What others are saying
N. T. Wright, Jesus and the Victory of God, (London: SPCK, 1996), 433–434 (emphasis original):
Fasting in this period was not, for Jews, simply an ascetic discipline, part of the general practice of piety. It had to do with Israel’s present condition: she was still in exile. More specifically, it had to do with commemorating the destruction of the Temple. Zechariah’s promise that the fasts would turn into feasts could come true only when YHWH restored the fortunes of his people. That, of course, was precisely what Jesus’ cryptic comments implied:
“The wedding guests cannot fast while they have the bridegroom with them, can they? As long as they have the bridegroom with them, they cannot fast” [Mark 2:19] …
In other words, the party is in full swing, and nobody wants glum faces at a wedding. This is not a piece of ‘teaching’ about ‘religion’ or ‘morality’; nor is it the dissemination of a timeless truth. It is a claim about eschatology. The time is fulfilled; the exile is over; the bridegroom is at hand. Jesus’ acted symbol, feasting rather than fasting, brings into public visibility his controversial claim, that in his work Israel’s hope was being realized; more specifically, that in his work the Temple was being rebuilt. Those who had got so used to living in exile that they could not hear the message of liberation were deaf indeed.
Scot McKnight, Sermon on the Mount, The Story of God Bible Commentary (Zondervan, 2013) on Matthew 6:16-18:
There is more to what Jesus says about fasting than what is found here. One passage that deserves attention is Mark 2: 18– 22, where fasting is a response to kingdom hope. Jesus declares that his disciples will fast as a way of yearning for God’s glory, for God’s kingdom, for God’s justice, and for God’s peace.
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