Fasting was a common practice among Israelites in both Old and New Testament times. People went without food or drink for a period, usually for some religious purpose. It may have been to express sorrow (1 Samuel 31:13; 1 Kings 21:27; Nehemiah 1:4), repentance (1 Samuel 7:6; Joel 2:12; Daniel 9:3-4) or sincerity in prayer (2 Chronicles 20:3-4; Ezra 8:23).
The only official fast according to the Jewish law was the annual Day of Atonement (assuming that ‘to afflict yourselves’ means ‘to fast’; Leviticus 23:27). The Jews later introduced a series of fasts to mourn the destruction of Jerusalem by Babylon in 587 BC (Zechariah 8:19). Because of the association of fasting with mourning, Jesus’ disciples did not fast while he was with them. That was a time of joy. They fasted only when he was taken from them and killed; but their sorrow was turned into joy at his resurrection (Luke 5:33-35).
Both Old and New Testaments speak of those who fasted insincerely. Some people made a show of their fasting, thinking they were impressing others, and in particular impressing God; but they were only inviting God’s condemnation (Isaiah 58:3-5; Matthew 6:16-18; Luke 18:12). By contrast, God approved of true fasting, whether individual or collective, when it was combined with genuine prayer (Matthew 4:1-4; Luke 2:37; Acts 13:2-3).
The Bible gives no explanation of the practical purpose of fasting. Examples of fasting in the New Testament show that it accompanied prayer when people faced unusually difficult tasks or decisions, or met unusually strong opposition from Satan. The purpose of the fast may have been to separate them as much as possible from the common affairs of everyday life. This would enable them, without distraction, to concentrate all their spiritual powers on the important issues before them.