Mark 2:19
And Jesus said unto them, Can the children of the bridechamber fast, while the bridegroom is with them? as long as they have the bridegroom with them, they can not fast. And Jesus said unto them, Can the children of the bridechamber fast, while the bridegroom is with them? as long as they have the bridegroom with them, they can not fast.
The bridegroom is Christ Himself present with His disciples, and the children of the bridechamber are the disciples themselves. While He is with them they cannot fast and mourn, for joy rather than fasting and mourning is fitting at such a time. Their joy is fitting because they have God with them, walking and talking with the Majesty of Heaven and having the Prince of Peace in their midst. They believe in Him, trust and love Him, are taught by Him daily, and receive daily mercies and blessings, which is an occasion for joy greater than any human enterprise.
They are not to mourn and fast in the same way as the Pharisees, so Pharisee-like mourning and fasting does not belong to that time. Mourning belonged instead to those who rejected the Saviour and chose bondage and darkness rather than freedom and light, though the treasure of Heaven was entrusted to them for a time.
The saying looks forward to days when the bridegroom would be taken away, when days of trial and temptation come and His presence and the Comforter are not clearly discerned, and then mourning and fasting become fitting. That taking away is His arrest, humiliation, crucifixion, and death as He approaches the cross and descends into humiliation. He is seen in the hands of wicked men, rejected by His own nation clamoring for His blood, crowned with thorns, clothed in the purple robe, mocked and struck with the reed, set aside for the murderer Barabbas instead of taking David's throne, scourged and lifted on the cross dying as a malefactor, when the disciples' hopes of eternal life seem centered in One so treated. Then their faith is tried and their hope and courage fail, giving cause to mourn and fast.
After He returned to Heaven and left His disciples to meet alone the unbelief and darkness of the world, it would be fitting for the church to fast and mourn until her absent Lord returns the second time.