old and new wineskins, old and new cloth

Right now, sorrow and fasting were frankly incongruous. The promised Messiah, the heavenly Bridegroom, was among them.
The truth, Jesus says, is that with the dawning of the kingdom, the traditional structures of life and forms of piety would change. It would be inappropriate to graft the new onto the old, as if the old were the supporting structure — in precisely the same way that it is inappropriate to repair a large rent in an old garment by using new, unshrunk cloth, or use old and brittle wineskins to contain new wine still fermenting, whose gases will doubtless explode the old skin. The old does not support the new; it points to it, prepares for it, and then gives way to it. Thus Jesus prepares his disciples for the massive changes that were dawning.

- Carson, For the Love of God, Vol. 1, commenting on Mark 2:18-22