Summary: Jesus explains why his disciples don't fast by comparing their situation to a wedding feast, where fasting would be inappropriate. He uses the metaphor of old garments and wineskins to illustrate the incompatibility of his new teachings with old traditions. Jesus suggests that new practices, like new wine, require new frameworks.
The disciples of John and of the Pharisees were accustomed to fast. People came to him and objected, “Why do the disciples of John and the disciples of the Pharisees fast, but your disciples do not fast?”
Jesus answered them, “Can the wedding guests fast while the bridegroom is with them? As long as they have the bridegroom with them they cannot fast. But the days will come when the bridegroom is taken away from them, and then they will fast on that day.
No one sews a piece of unshrunken cloth on an old cloak. If he does, its fullness pulls away, the new from the old, and the tear gets worse. Likewise, no one pours new wine into old wineskins. Otherwise, the wine will burst the skins, and both the wine and the skins are ruined. Rather, new wine is poured into fresh wineskins.”