What does Mark 2:20 mean?Here, in the initial days of the ministry in Galilee, Jesus makes His first allusion to the fact that He will one day leave His followers behind. Jesus' statement also infers that there are appropriate reasons to fast.
Matthew 6:16–18 suggests that fasting for self-discipline and as an expression of piety is acceptable, as long as it is done in the right way. The Pharisees—legalistic religious leaders—fast openly, letting everyone know how spiritual they are. Jesus says that the attention they receive by other men will be their only reward. If we wish to be blessed by God, we must do things for Him, not for the acclaim of the world.
In Luke 4:1–2, Jesus fasts for forty days before Satan tempts Him. Fasting is certainly appropriate for preparing for a hardship, but it's important to note that Jesus only fasts to such an extreme once. He does not make a habit of it.
Early church leaders fasted before making important decisions. The church elders at Antioch fasted before sending Barnabas and Paul out on a mission trip (Acts 13:1–3). In return, Barnabas and Paul fasted before appointing elders in the new churches (Acts 14:21–23).
So fasting, whether personal or in a group, is appropriate for Christians but it is not specifically ordained. Fasting should be voluntary and done in a way that brings us closer to God. We should be respectful of health concerns that would make fasting from all food unwise; the Bible suggests there are other things we can temporarily avoid to practice discipline and make time to seek God (1 Corinthians 7:1–5).