Matthew 9:15
And Jesus said unto them, Can the children of the bridechamber mourn, as long as the bridegroom is with them? but the days will come, when the bridegroom shall be taken from them, and then shall they fast. And Jesus said unto them, Can the children of the bridechamber mourn, as long as the bridegroom is with them? but the days will come, when the bridegroom shall be taken from them, and then shall they fast.
The question was a complaint from John's disciples united with the Pharisees about why Jesus' disciples did not fast. John's disciples were fasting and mourning often because John was in prison, and they had not fully accepted Jesus as the world's Redeemer. They thought He needed reform because He did not act in every particular as John did, and because His disciples were molded differently from themselves and from the scribes and Pharisees. While they mourned and fasted they saw Him sitting and eating with publicans and sinners, misinterpreted His object, and condemned His practice.
Jesus is the Bridegroom and His disciples are the children of the bridechamber, so to have Him with them was to have the presence of God with them. While the Bridegroom was with them mourning and fasting were not appropriate, for He was everything to them and the time was one of joy. His presence brought the world God's gift and light and brought them daily blessings, and they believed in Him, trusted Him, loved Him, and were daily taught by Him. Their work then was to be catching the rays of light from Him and learning the spiritual nature of His kingdom and the grace of His character, so that they could work when He should leave them.
The Bridegroom being taken from them means His approach to the cross and descent into humiliation through betrayal and crucifixion. Then He in whom their hopes of eternal life were centered would be in the hands of wicked men. His own nation would clamor for His blood, while Herod and his soldiers plaited the crown of thorns for His brow, clothed Him in the purple robe, mocked Him and struck Him with the reed, scourged Him as the worst of criminals while Barabbas was chosen in His place, and lifted Him up to die as a malefactor on the cross.
After His resurrection and ascension their sorrow was to become joy. Though no longer present with them in person, He would remain with them through the Comforter, and they were to look by faith to His ministry in the heavenly sanctuary and rejoice in the Holy Spirit's presence. When the Bridegroom was taken away, then mourning and fasting would be fitting and consistent. The disciples would have cause for it when their faith was tried and their hope and courage failed, and fasting would again be fitting in later days of trial and temptation when Christ was not personally with them and the presence of the Comforter was not clearly discerned, as the church faced the unbelief and darkness of the world until His second coming after His return to heaven.