The Heavenly Bridegroom Has Come To Call His Bride and Provide New Truth (2:18-22).
In this passage Jesus defends His disciples right not to fast. John's disciples and the Pharisees were fasting, seemingly at a season when fasting was expected of pious men. His point is that fasting indicates mourning and sorrow for sin as men hope for a better future, while for His disciples that is not necessary because a better future has already come. It was not right therefore that they fast, because the One is now among them Who will fulfil all God's promises so that they should be rejoicing. For He Himself has come as the heavenly Bridegroom promised in the Scriptures, come to be united with His bride (compare Matthew 12:49-50; Hebrews 2:11 where He is their Elder Brother). That is why what they should be doing is rejoice. He then goes on to point out that what He has brought for men replaces the old rather worn out teaching. He is referring, not to the Scriptures themselves, which did not need to be replaced, but to what men had made of those Scriptures, which did.
Analysis of 2:18-22.
a And John's disciples and the Pharisees were fasting, and they come and say to him, “Why do John's disciples and the disciples of the Pharisees fast, and yet your disciples do not fast?” (Mark 2:18).
b And Jesus said to them, “Can the sons of the bridechamber fast while the Bridegroom is with them? As long as they have the Bridegroom with them they cannot fast” (Mark 2:19).
c “But the days will come when the Bridegroom will be taken away from them, and then they will fast in that day” (Mark 2:20).
b “No man sews a piece of undressed cloth on an old piece of clothing, otherwise that which should fill it up (or ‘the patch' - to pleroma) takes away from it, the new from the old, and a worse tear is made” (Mark 2:21).
a “And no man puts new wine into old wineskins, or else the wine will burst the skins, and the wine perishes, and the skins. But they put new wine into fresh wineskins” (Mark 2:22).
Note that in ‘a' the question is why Jesus' disciples do not behave like other dedicated religious men, and in the parallel the answer is because new wine must be put into fresh wineskins. In ‘b' Jesus says that the Bridegroom's special friends cannot fast while the Bridegroom is with them, because by His presence a new situation has arisen and the old methods will spoil the new, and in the parallel no one tries to repair old clothing with a patch of new cloth, again because they are incompatible. Centrally in ‘c' is what the future holds, that the Bridegroom will eventually be forcibly removed. Then indeed the disciples will fast (compare John 16:20).