Matthew 9:14 Then the disciples of John came to him, saying, "Why do we and the Pharisees fast, but your disciples do not fast?" 15 And Jesus said to them, "Can the wedding guests mourn as long as the bridegroom is with them? The days will come when the bridegroom is taken away from them, and then they will fast. 16 No one puts a piece of unshrunk cloth on an old garment, for the patch tears away from the garment, and a worse tear is made. 17 Neither is new wine put into old wineskins. If it is, the skins burst and the wine is spilled and the skins are destroyed. But new wine is put into fresh wineskins, and so both are preserved."
The practice of the Pharisees was to fast twice a week (Luke 18:12). The fast was meant to be a way of humbling oneself before God for God resists the proud, but gives grace to the humble (James 4:6). The Pharisees fasted for all people to see how righteous they were. However, the Pharisees did not fast to humble themselves before God. Jesus rebuked the practice of the Pharisees and told them to not let people see they were fasting and to truly fast to humble themselves before God (Matthew 5:16-18). In the Old Testament there was one day a year only that God instructed the people to fast, the Day of Atonement (Leviticus 23:27). There were also other times of fasting gain God's help. Joel, the prophet, called his people to fast as a way of humbling themselves before God in the face of impending judgment (Joel 1:14; 2:15). Ezra proclaimed a fast to humble the returning exiles before God to gain His favor and protection (Ezra 8:21). Esther proclaimed a fast to humble the Jews before to gain His favor as she went in to the king to make a request to save the Jewish nation (Esther 4:16). The Jews in exile practiced fasting in the 4th, 5th, 7th, and 10th month to humble themselves before God so He would return them to the promised land. God spoke through Isaiah to tell His people an external fast without internal obedience is not humbling oneself Isaiah 58:3-6). Fasting was merely a way to humble oneself before God to gain His grace to help in times of need.
Jesus said that since He was present with the disciples, they did not need to fast, but rather to feast since He was with them. He said they would fast when He was taken away by His death on the cross and before He came to dwell in them on the day of Pentecost when the Holy Spirit, the Spirit of Christ was poured out on the people who believed in Him. In Matthew 28:20 Jesus said He would be with us until the end of the age. Romans 8:9-11 and Colossians 1:27 are two places that inform us Christ is in us and thus with us.
Jesus told us that since He died on the cross, rose from the dead, ascended into heaven and came to live in us that old practices would change. We relate to God in new ways in the New covenant God has with us in Christ. We don't offer animal sacrifices, but spiritual sacrifices (Hebrews 13:15-16). We don't fast to humble ourselves, we acknowledge our dependence upon God and obey Him by faith in Jesus. The Apostle Paul explains this new way of serving God in Christ in Romans 14. What counts now is loving God and people. John explains how we express this love in 1 John 5:2-3. We are able to do this by grace through faith (2 Corinthians 12:9; Galatians 2:20).
So how about you? Are you seeking to humble yourself before God by external means only or are you acknowledging your dependence upon the Lord by obeying Him by grace through faith? We have received grace to be pardoned from the penalty of sin and grace to be free from slavery to sin. We access this grace in our daily living by faith in Jesus. We attempt to obey Him and fulfills our attempt with His power.