We know by a casual reading of Scripture that fasting, intentional abstaining from eating for a period of time, was part the spiritual life.
To correct the misuse of fasting where men did it to draw attention to themselves by flaunting their piety, Jesus said, “16 Whenever you fast, do not put on a gloomy face as the hypocrites do, for they neglect their appearance so that they will be noticed by men when they are fasting. Truly I say to you, they have their reward in full. 17 “But you, when you fast, anoint your head and wash your face 18 so that your fasting will not be noticed by men, but by your Father who is in secret; and your Father who sees what is done in secret will reward you“, Mt 6:16ff.
I take note of the fact that Jesus did not say, “If you fast”, but He said, “Whenever you fast”, which implies to me that pious people are going to fast. Just as there’s no question that pious people are going to give and pray, similarly are people of faith going to fast.
When to fast is not set by others. It’s personal and depends on the circumstances. It says that the disciples of John the Baptist approached Jesus asking Him, “Why do we and the Pharisees fast, but Your disciples do not fast?” Mt 9:14. Jesus’ answer shows that that the circumstances have to be right for fasting. Just as it’s not right for a funeral dirge to be played at a wedding, just so is it not proper, according to Jesus, for His disciples to be fasting at that present time. Later they would fast.
“But the days will come when the bridegroom is taken away from them, and then they will fast”, Mt 9:15b.
The circumstances would determine the time for fasting. When the judgment of God was coming and there was only a little time for gaining His favor, God said for the people to fast. Joel 2 is talking about God’s judgment coming upon Israel and holds out a promise that the favor of the Lord may still be won.
“12 “Yet even now,” declares the LORD,
“Return to Me with all your heart,
And with fasting, weeping and mourning;
13 And rend your heart and not your garments.”
Now return to the LORD your God,
For He is gracious and compassionate,
Slow to anger, abounding in lovingkindness
And relenting of evil.”
The “formula” of fasting and rending the garments is seen in other places as well. In Nineveh, as the people responded to the preaching of Jonah they turned from sin with fasting, Jonah 3:5; cf Joel 1:14; Ps 35:13.
During times of repentance it would be a good time to withhold from feasting. Coinciding with the prayers of repentance, it seems appropriate that the repentant sinner not think of eating as part of the devotion, Acts 9:9. During times of change or when wisdom from the Lord is sought after, it would be a good time for fasting. When Paul and Barnabas appointed Elders in the congregations, they did so with prayer and fasting, Acts 13:3. And during a time of mourning, as when the disciples would not have their Lord when He was crucified, this was the time Jesus said His disciples would fast. So during times of repentance, seeking wisdom, and mourning there are examples of disciples fasting. This would suggest there are many opportunities for fasting in the life of a godly person.
When to fast is a matter of personal choice. Kings or Elders may “proclaim a fast to the Lord”, but it’s a matter of personal choice as is any act of devotion to God. When you fast, make sure it is not done for vain glory. Let fasting, when you decide to do it, be part of the sincere drawing near to God.
As an aside, fasting can also be done for non-religious reasons. As a practical matter, for every buffet line we walk through there needs to be balance which means a time of pushing away from the plate.