14Then the disciples of John came to Him, saying, "Why do we and the Pharisees fast often, but Your disciples do not fast?"
15And Jesus said to them, "Can the friends of the bridegroom mourn as long as the bridegroom is with them? But the days will come when the bridegroom will be taken away from them, and then they will fast. 16No one puts a piece of unshrunk cloth on an old garment; for the patch pulls away from the garment, and the tear is made worse. 17Nor do they put new wine into old wineskins, or else the wineskins break, the wine is spilled, and the wineskins are ruined. But they put new wine into new wineskins, and both are preserved."
Back in Matthew 6:16-18, I tried to understand the reason behind fasting, though that text dealt with how to fast for God, not why. I was coming to the conclusion that fasting is one way to develop a closer relationship with God. This fits in with Jesus' answer that there is no need to fast when Jesus is present. But according to this response from Jesus, it seems that fasting is also one form of mourning. So was fasting only used as a way to mourn?
There may have been many laws governing fasting at that time. The disciples of John and the Pharisees noticed that Jesus and His disciples weren't following these laws. I think Jesus' answer had more to do with the observances of all the old laws than just what to do about the laws of fasting. Is Jesus getting rid of all the old laws? Should fasting go away entirely? No, Jesus foretells that He will one day be taken away from them, then they will once again fast.
But what of the old laws? Back in Matthew 5:17, Jesus said He did not come to destroy the law but to fulfill it. With the law fulfilled, Jesus is preparing a new covenant with us. This new covenant will not simply be a matter of adding a few new laws to the old ones, that would only make matters worse, just as patching an old garment with an unshrunk piece of cloth would only make the tear worse. The laws would need to be redone.
The other point that Jesus makes is for those who try to keep the old laws while trying to observe the new laws. It would be impossible to keep both, thus not being able to keep either one, just as putting new wine into old wineskins would cause the wineskins to break ruining both the wineskins and the wine.
I know how hard it is to change. Too often we do things a certain way just because that is the way it has always been done. It is the way we were taught to do things and we respected the ones who taught us. It is hard to let go of what had always seemed so important. But Jesus is telling them they will need to let go of the old laws and prepare for a new covenant. Jesus is telling of a great change coming. Are they ready for it? Are we ready for it?