Why the Parable?
Jesus' story of new wine into old wineskins is the tenth parable recorded in the book of Matthew. It was offered as part of his response to the question of why his disciples did not fast like the disciples of John the Baptist or the Pharisees (Matthew 9:14).
"Are the children of the bridechamber (the disciples) able to mourn while the bridegroom (symbolizing the Lord) is with them? But the days will come when the bridegroom shall be taken away from them, and then they shall fast . . .
"Neither do they put new wine into old wineskins; otherwise the wineskins will burst, and the wine will spill out, and the wineskins will be destroyed; but they put new wine into new wineskins, and both are preserved together." (Matthew 9:15, 17, HBFV throughout, see also Mark 2:22 and Luke 5:37 - 38).
The Lord's initial response to those who quizzed him wasn't that fasting was not needed by his disciples. His disagreement centered on the assumption that his followers should fast while he was among them.
The disciples didn't need to fast to draw close to God as long as Jesus, who was God in the flesh, was alive and interacting with them on a daily basis. They would need to do so, however, when this level of his relationship with them ended when he died and was resurrected from the dead. After his initial response he offered his parable of new wine and old wineskins to further elaborate his point.
A Well Known Behavior
The behavior highlighted in the parable of new wine and old wineskins was easy enough for Jesus' audience to understand. Winemaking required picking the grapes and pressing the juice out by treading on them (see Isaiah 63:1 - 3 and Revelation 14:19 - 20). The juice was then strained through a filter and allowed to naturally ferment for about a week.
After an initial period of fermentation the liquid was put into storage containers like wineskins where it experienced its secondary fermentation period. These holders of liquid were usually made from the skin or cleansed stomach of a goat or sheep, although ox or camel skin may have also been used (International Standard Bible Encyclopedia). After forty days the wine was considered fit as a drink offering to God (1906 Jewish Encyclopedia).
New wineskins were able to expand without breaking as the wine placed within them continued to produce gases that were a natural part of the fermentation process. Old ones, in contrast, had aged to the point where they could no longer expand. Their inability to adapt to the stresses placed on them made them prone to bursting and wasting the precious liquid inside them.
But new wine must be put into new skins, and both will be preserved together. (Luke 5:38).
The disciples, at the time of the parable, had only been with Jesus for less than a year (Matthew was called only a few months prior, see Matthew 9:9). They also only had the Holy Spirit with them but not in them (John 14:17). Jesus knew that requiring the austere practice of fasting on such still carnal "spiritual babies" (see Matthew 11:25, 1Corinthians 3:1) would have been a bit too much and could have caused some of them to "burst!"
On Pentecost, a little more than two years after the new wine into old wineskins parable was given, the disciples received the spiritual power promised them (Acts 2). They were changed from "old wineskins" into those that were new. They could now begin to comprehend the spiritual depth of Jesus' teachings and fully benefit from practices such as fasting.