Fasting was an accepted part of everyday life in Old Testament times. Bear in mind that Israel was not a political state, but a theocracy, which is a religious state in which the Law and will of God were preeminent.
The first reference to fasting is in the Book of Judges, Judges 20:26. The last reference is in the Book of Zechariah, and devout Jews fasted, Zechariah 8:19. Most of the fasting was undertaken voluntarily and was not undertaken at the command of God, but devout Jews undertook to fast for at least two reasons. Not for health reasons, but for the following reasons.
1. They believed it was a way of attracting the attention of God. If they fasted, they thought that God noticed them.
2. They thought that if they fasted, God would be prepared do something about the situation that had caused them to fast.
If you think about this second reason, you will see that a man thought fasting had influenced God to act; it was very easy for him to imagine that he, personally, was someone special! Matthew 6:16-18.
The reality, although, through the centuries, the Jews, especially after the Babylonian Captivity, introduced fasts for a whole range of reasons, but only one fast was specifically commanded by God, and that was the fast associated with the Day of Atonement, the most important and solemn Day in their religious year.
In Leviticus 16:29, we find the expression, ‘deny yourselves’ or ‘afflict your souls’. This is the expression for fasting, and this was the only fast that the Jews observed faithfully every year.
When we examine the New Testament, it surprises some people to find that the Lord only mentioned fasting twice, Matthew 6:16-18 / Mark 2:18-22. Notice that both passages above record Jesus’ response to the practice of that time.
But also notice, although about sixteen times He says, ‘it was said by those of old-time, but I say to you’, Jesus doesn’t use these words because this kind of fasting about which He was speaking wasn’t covered by the Mosaic Law, but because it was something that the people had taken on themselves in the old law.
In the Book of Acts, Luke records that the church in Antioch sent Barnabas and Paul on the First Missionary Journey, with prayer and fasting. In the next chapter, they fasted in connection with the appointment of elders, Acts 13:1-3. Please note that the whole church didn’t fast, it was only those mentioned, ‘Barnabas, Simeon called Niger, Lucius of Cyrene, Manaen and Saul,’ Acts 13:1.
In 1 Corinthians 7:1-5, Paul mentions sexual fasting, but neither here nor anywhere else does he impose it as a command. In 2 Corinthians 6:5 and 2 Corinthians 11:27, he refers to what he suffered for the sake of the Gospel and speaks of times when he went without food. But this wasn’t because he was ‘fasting’, but because he had no food to eat!
The answer to the question, should a Christian fast? is therefore, yes! If they want to! But remember that fasting, like ‘bodily exercise,’ may do a little good, but ‘godliness is profitable for all things!’ 1 Timothy 4:8.